feat(app): add flow diagnostics and refine interface

Improve failure recovery visibility, strengthen account-session handling, and make the cross-platform interface more consistent.

OSGKeyboardMac/MacTheme.swift

@@ -30,6 +30,7 @@ enum MacSystemPalette {
         ThemePalette(
             background: resolved(dark ? darkBackground : warmBackground, dark: dark),
             surface: resolved(dark ? darkSurface : warmSurface, dark: dark),
+            formSurface: resolved(dark ? darkFormSurface : warmFormSurface, dark: dark),
             surfaceElevated: resolved(dark ? darkElevated : warmElevated, dark: dark),
             surfaceMuted: resolved(dark ? darkMuted : warmMuted, dark: dark),
 
@@ -45,14 +46,14 @@ enum MacSystemPalette {
             textPrimary: resolved(.labelColor, dark: dark),
             textSecondary: resolved(.secondaryLabelColor, dark: dark),
             textTertiary: resolved(.tertiaryLabelColor, dark: dark),
-            textOnAccent: Color.white,
+            textOnAccent: OSGColor.fixedLightContent,
 
             divider: dark
-                ? Color.white.opacity(0.08)
-                : Color.black.opacity(0.06),
+                ? OSGColor.macDarkDivider
+                : OSGColor.lightDivider,
             dividerStrong: dark
-                ? Color.white.opacity(0.12)
-                : Color.black.opacity(0.10),
+                ? OSGColor.macDarkDividerStrong
+                : OSGColor.lightDividerStrong,
 
             recordRed: resolved(.systemRed, dark: dark),
             recordBlue: resolved(.systemBlue, dark: dark)
@@ -62,13 +63,15 @@ enum MacSystemPalette {
     // MARK: - Warm Light-mode surfaces (matched to iOS `Palette.light`)
 
     /// #F2F1EE — warm gray page background.
-    private static let warmBackground = NSColor(srgbRed: 0.949, green: 0.945, blue: 0.933, alpha: 1)
+    private static let warmBackground = NSColor(OSGColor.lightBackground)
     /// #FCFBF9 — warm off-white card/control surface.
-    private static let warmSurface = NSColor(srgbRed: 0.988, green: 0.984, blue: 0.976, alpha: 1)
+    private static let warmSurface = NSColor(OSGColor.lightSurface)
+    /// #FCFBF9 — forms retain the ordinary card fill in light mode.
+    private static let warmFormSurface = warmSurface
     /// #EBEAE7 — slightly recessed elevated surface.
-    private static let warmElevated = NSColor(srgbRed: 0.922, green: 0.918, blue: 0.906, alpha: 1)
+    private static let warmElevated = NSColor(OSGColor.lightSurfaceElevated)
     /// #EEEDE9 — muted fill between background and surface.
-    private static let warmMuted = NSColor(srgbRed: 0.933, green: 0.929, blue: 0.918, alpha: 1)
+    private static let warmMuted = NSColor(OSGColor.lightSurfaceMuted)
 
     // MARK: - Dark-mode surfaces (Apple standard elevated grays)
     //
@@ -78,13 +81,15 @@ enum MacSystemPalette {
     // clearly elevated above the background — mirroring the iOS dark palette.
 
     /// #1C1C1E — page background.
-    private static let darkBackground = NSColor(srgbRed: 0.110, green: 0.110, blue: 0.118, alpha: 1)
+    private static let darkBackground = NSColor(OSGColor.macDarkBackground)
     /// #2C2C2E — card / control surface, clearly lighter than the background.
-    private static let darkSurface = NSColor(srgbRed: 0.173, green: 0.173, blue: 0.180, alpha: 1)
+    private static let darkSurface = NSColor(OSGColor.macDarkSurface)
+    /// #343438 — interactive form fill between cards and elevated chrome.
+    private static let darkFormSurface = NSColor(OSGColor.macDarkFormSurface)
     /// #3A3A3C — elevated fill for selected / raised chrome.
-    private static let darkElevated = NSColor(srgbRed: 0.227, green: 0.227, blue: 0.235, alpha: 1)
+    private static let darkElevated = NSColor(OSGColor.macDarkSurfaceElevated)
     /// #242426 — muted fill between background and surface.
-    private static let darkMuted = NSColor(srgbRed: 0.141, green: 0.141, blue: 0.149, alpha: 1)
+    private static let darkMuted = NSColor(OSGColor.macDarkSurfaceMuted)
 
     /// Resolves a (possibly dynamic) AppKit colour to its concrete value under
     /// the requested appearance, so the two static palettes differ by value.