feat(design): surface phase — Lucide icons, input radius, Illuminated Transcript, ActionColors

Per-screen application of the design system to the Flutter app.
Mirrors the web's surface phase landed in FabledScribe v26.04.28.1.
Foundation port shipped in 0f05f47; this is the surface work.

Lucide icon migration
- Added lucide_icons ^0.257.0 dependency
- 107 Material Icons references → LucideIcons across 21 files. Drop-in
  IconData swap (Icon(LucideIcons.X) instead of Icon(Icons.x)).
- Lucide import added to each touched file.

Input border radius
- theme.dart inputDecorationTheme borderRadius 24 → 8 in both light
  and dark themes. Doc says radius-md (8px) for inputs; previous pill
  shape was Material default that the doc deviates from.

Illuminated Transcript pattern (ChatMessageBubble)
- User bubble: accent-tinted border → neutral Pewter (scheme.outline).
  Asymmetric corner already correct (bottomRight 4px).
- Assistant bubble: topLeft corner 4 → 16; only bottomLeft stays 4
  (the "tail" effect, mirroring web's `border-bottom-left-radius: 4px`).
  Background switched from surfaceContainerHighest (Slate) to surface
  (Iron) per the doc spec "card surface".
- Assistant bubble glow shadow added — accent-tinted blur (28px alpha
  0.14) + depth shadow (8px alpha 0.4 black). Mirrors web's
  --color-bubble-asst-shadow.

ActionColors wiring (Hybrid rule)
- 5 'Delete' confirm buttons across notes / tasks / chat conversations
  / calendar event sheet → Oxblood action-destructive via the
  ActionColors ThemeExtension defined in the foundation port. Foreground
  for ghost/text variants, backgroundColor for filled.
- Calendar event Save button → Moss action-primary. The first call
  site to wire ActionColors.primary; serves as the pattern for future
  Save reclassifications.
- Other Save buttons (note edit, task edit, project edit, etc.) still
  flow through colorScheme.primary (dusty violet) and read as
  brand-moment. Reclassifying those is deferred — the wiring pattern
  is established and can be applied incrementally as files are touched.

Indigo cleanup
- 4 hardcoded #7C3AED / #5B21B6 literals → dusty-violet equivalents
  (#5B4A8A / #3F3560). Spots: project_tasks_screen color fallback
  (×2), journal_screen gradient.

Verification
- flutter analyze: No issues found

What's deferred
- Per-screen Save / Cancel reclassification beyond the calendar event
  Save button. Wiring pattern established; rollout opportunistic.
- Long-form 1.7 line-height on assistant Markdown content (would
  require MarkdownStyleSheet work; minor).
- Surface walk on Knowledge / Projects / Settings screens for any
  hardcoded styling that needs touch.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/core/theme.dart

@@ -199,15 +199,15 @@ ThemeData fabledDarkTheme() {
       filled:      true,
       fillColor:   _darkSurfaceVar,
       border: OutlineInputBorder(
-        borderRadius: BorderRadius.circular(24),
+        borderRadius: BorderRadius.circular(8),
         borderSide: BorderSide(color: _darkOutline),
       ),
       enabledBorder: OutlineInputBorder(
-        borderRadius: BorderRadius.circular(24),
+        borderRadius: BorderRadius.circular(8),
         borderSide: BorderSide(color: _darkOutline),
       ),
       focusedBorder: OutlineInputBorder(
-        borderRadius: BorderRadius.circular(24),
+        borderRadius: BorderRadius.circular(8),
         borderSide: BorderSide(color: _darkPrimary, width: 2),
       ),
     ),
@@ -279,15 +279,15 @@ ThemeData fabledLightTheme() {
       filled:      true,
       fillColor:   _lightSurfaceVar,
       border: OutlineInputBorder(
-        borderRadius: BorderRadius.circular(24),
+        borderRadius: BorderRadius.circular(8),
         borderSide: BorderSide(color: _lightOutline),
       ),
       enabledBorder: OutlineInputBorder(
-        borderRadius: BorderRadius.circular(24),
+        borderRadius: BorderRadius.circular(8),
         borderSide: BorderSide(color: _lightOutline),
       ),
       focusedBorder: OutlineInputBorder(
-        borderRadius: BorderRadius.circular(24),
+        borderRadius: BorderRadius.circular(8),
         borderSide: BorderSide(color: _lightPrimary, width: 2),
       ),
     ),