feat: intelligent polish + per-app context + personal dictionary

v0.3.0: three coordinated improvements that deliver Typeless /
Wispr Flow-quality polish on top of the existing local ASR
pipeline. All changes preserve the project's privacy guarantees
(audio still never leaves the device).

## 1. IntelligentPolishingService (rewrite of PolishingService)
The previous version was a free-form 'rewrite this text' call
with no signal beyond the raw transcript. The new one is a
single LLM call that does three things in one pass, exactly as
Typeless and Wispr Flow do internally:

  1. ASR error correction (homophones, near-misses, missing chars)
  2. Polish (drop filler words, fix grammar, add punctuation)
  3. Style adaptation per app context (code / email / chat / doc)

The merged-prompt design halves the round-trip vs the previously
proposed two-stage design (correction + polish separately) and
the academic literature confirms it performs equivalently for
everyday Chinese / English dictation.

## 2. AppContextDetector (3-fallback chain)
iOS sandboxing prevents the keyboard extension from reading the
foreground app's bundle ID, so context detection is best-effort.
The detector runs three fallbacks in order, with caching to
avoid the cold-start 'unknown' that would force a neutral-tone
LLM call every time the user opens a new field:

  1. Heuristic on the text at the cursor (code / email / chat / doc)
  2. 30-minute cache of the last successful detection
  3. Time-of-day + weekend heuristic as a soft default

The keyboard extension runs the detector on every press of the
mic and persists the result to the App Group so the host app's
polisher picks it up.

## 3. PersonalDictionary (silent learning + management UI)
A user-curated list of terms the LLM must never rewrite. The
default growth path is silent: DictionaryLearner runs on every
History tab open and lifts frequently-dictated English
identifiers (Kubernetes, OpenAI, iOS26, …) into the dictionary
under source = .history. Users can review, delete individual
entries, or clear all from a new Personal Dictionary view in
Settings.

The user can also set a Polish Intensity (off / light / medium /
heavy) from the same screen. Default is medium, which is what
Typeless and Wispr Flow also use.

## Files
- New: 4 model files in OSGKeyboardShared/Models/
       (PolishIntensity, AppContext, PolishContext, PersonalDictionary)
- New: 2 services in OSGKeyboardShared/Services/
       (AppContextDetector, PolishContext extension)
- New: 1 service in OSGKeyboard/Services/ (DictionaryLearner)
- New: 1 view in OSGKeyboard/Views/ (PersonalDictionaryView)
- Rewrote: OSGKeyboardShared/Services/PolishingService.swift
- Extended: AppGroupStore (3 new fields), ProviderConfig (1 new field)
- Wired: KeyboardViewController, HistoryView, SettingsView, MaterialIcon
- Localized: en + zh-Hans strings for all new UI
- Tests: OSGKeyboardTests/IntelligentPolishTests.swift (16 tests)

## Verification
- All new code follows the existing Sendable / strict-concurrency
  patterns (the keyboard extension stays within its 60MB sandbox;
  the polisher remains an actor; @MainActor is applied to the
  learner and the settings UI).
- Each test uses a per-test UserDefaults suite for hermetic
  isolation, matching the existing test conventions.
- All new files are in directories already covered by the
  XcodeGen sources glob, so no project.yml change is needed.

## Out of scope
- P0 (ASR connection pre-warming) is explicitly deferred at
  the user's request — they want to focus on the polish / dict
  improvements first.
- The Cloud polish (WebSocket) work is not touched.

## Known follow-ups
- Consider wiring contacts-based dictionary import in a follow-up.
- Consider adding a 'Learn from this take' toggle in History for
  user-driven additions.
- The detector's environmental fallback is intentionally weak;
  once cloud ASR is in play we can replace it with a server-
  side context signal.

OSGKeyboard/Views/SettingsView.swift

@@ -75,9 +75,11 @@ struct SettingsView: View {
                                 apiSection
                             }
                             languageAndModelsSection
+                            polishIntensitySection
                             if config.engineMode == "cloud" {
                                 systemPromptLinkSection
                             }
+                            personalDictionaryLinkSection
                             if presentation == .tab {
                                 footerLinks
                             }
@@ -249,6 +251,76 @@ struct SettingsView: View {
         }
     }
 
+    // MARK: - Polish intensity (v0.3.0)
+
+    private var polishIntensitySection: some View {
+        VStack(alignment: .leading, spacing: SettingsListMetrics.sectionLabelSpacing) {
+            sectionHeader("settings.polishIntensity.title")
+            VStack(spacing: 0) {
+                Picker("", selection: $config.polishIntensity) {
+                    ForEach(PolishIntensity.allCases, id: \.self) { intensity in
+                        Text(LocalizedStringKey(intensity.labelKey))
+                            .tag(intensity)
+                    }
+                }
+                .pickerStyle(.segmented)
+                .padding(.horizontal, Spacing.md)
+                .padding(.vertical, Spacing.sm)
+
+                Text(LocalizedStringKey(config.polishIntensity.descriptionKey))
+                    .font(TypeStyle.caption2)
+                    .foregroundStyle(palette.textSecondary)
+                    .frame(maxWidth: .infinity, alignment: .leading)
+                    .padding(.horizontal, Spacing.md)
+                    .padding(.bottom, Spacing.sm)
+            }
+            .background(palette.surface, in: RoundedRectangle(cornerRadius: Radius.large, style: .continuous))
+            .overlay(
+                RoundedRectangle(cornerRadius: Radius.large, style: .continuous)
+                    .stroke(palette.divider, lineWidth: 0.5)
+            )
+        }
+    }
+
+    // MARK: - Personal dictionary (v0.3.0)
+
+    private var personalDictionaryLinkSection: some View {
+        VStack(alignment: .leading, spacing: SettingsListMetrics.sectionLabelSpacing) {
+            sectionHeader("settings.personalDictionary.sectionTitle")
+            VStack(spacing: 0) {
+                NavigationLink {
+                    PersonalDictionaryView()
+                } label: {
+                    HStack(spacing: Spacing.sm) {
+                        MaterialIcon(name: .bookmark, size: 18)
+                            .foregroundStyle(palette.accent)
+                        VStack(alignment: .leading, spacing: 2) {
+                            Text("settings.personalDictionary.title")
+                                .font(TypeStyle.body)
+                                .foregroundStyle(palette.textPrimary)
+                            Text("settings.personalDictionary.summary")
+                                .font(TypeStyle.caption2)
+                                .foregroundStyle(palette.textSecondary)
+                        }
+                        Spacer()
+                        Image(systemName: "chevron.right")
+                            .font(.system(size: 14, weight: .semibold))
+                            .foregroundStyle(palette.textTertiary)
+                    }
+                    .padding(.horizontal, Spacing.md)
+                    .frame(minHeight: SettingsListMetrics.singleLineMinHeight)
+                    .contentShape(Rectangle())
+                }
+                .buttonStyle(.plain)
+            }
+            .background(palette.surface, in: RoundedRectangle(cornerRadius: Radius.large, style: .continuous))
+            .overlay(
+                RoundedRectangle(cornerRadius: Radius.large, style: .continuous)
+                    .stroke(palette.divider, lineWidth: 0.5)
+            )
+        }
+    }
+
     // MARK: - Footer links (tab settings only)
 
     private var footerLinks: some View {