[JJC-20260618-005-A] Review-driven P0 polish

6 review-driven small fixes to the P0 commit series (e0b92ff / e93bab5 /
2e2d8e3 / 013c498). No behavior changes, no new features, no push yet.

Code:
- RED-1: Remove empty init() from OSGKeyboardApp; @StateObject is initialized
  inline and the only thing init() did was print a DEBUG log.
- RED-4: Re-add .preferredColorScheme(.dark) to the 3 keyboard extension
  #Preview blocks. Custom keyboards always render dark; the preview should
  match.
- RED-6: ThemedRoot #Preview blocks now use the new EnvironmentKey
  (\.themePalette) via a private ThemedPreviewContent, instead of hard-coding
  Palette.dark / Palette.light.
- BUG-5: ThemedRoot body now also fills the background with the active
  palette's background color (repeats the colorScheme ternary — accepted
  because body must be a single expression).

Docs:
- DOC-1: CHANGELOG [Unreleased] top note: this is a v0.1.0 → v0.1.1 polish,
  nothing removed, iOS 26 SpeechAnalyzer still 0.2.0.
- DOC-2: README + README.zh.md Limitations: explicit note for iOS 26+ users
  in v0.1.1.

Verified: xcodebuild Debug-iphonesimulator BUILD SUCCEEDED, 8/8 unit
tests pass on iPhone 17 sim (iOS 26.3.1).

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+> **Note: v0.1.1 polish** — this is a small follow-up to v0.1.0 focused on review-driven cleanup
+> (theme follow-up, ASR robustness, debug-print hygiene, docs). **No features are removed.**
+> The iOS 26 `SpeechAnalyzer` path remains deferred to 0.2.0 (see below); v0.1.1 users continue
+> to ship with the iOS 18 `SFSpeechRecognizer` path that shipped in v0.1.0. User experience is
+> unchanged from v0.1.0.
+
 ### Fixed
 - **Theme follows system appearance**: main App now renders a true light palette in light mode via `ThemedRoot` + `EnvironmentKey<ThemePalette>`. The keyboard extension deliberately stays dark (Apple's default) and now uses a transparent `.background(Color.clear)` so the system UI chrome shows through.
 - **Speech Recognition permission requested on first press**: added `NSSpeechRecognitionUsageDescription` to both targets' `Info.plist` and an explicit `SFSpeechRecognizer.requestAuthorization` call inside `pressBegan()`. Without these the iOS 18 ASR path silently returned `.denied` and the user heard nothing.