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/widgets/chat_message_bubble.dart

@@ -41,13 +41,16 @@ class ChatMessageBubble extends ConsumerWidget {
           maxWidth: min(MediaQuery.of(context).size.width * 0.82, 480),
         ),
         margin: const EdgeInsets.symmetric(vertical: 4, horizontal: 4),
+        // Illuminated Transcript pattern (mirrors web's ChatMessage.vue):
+        // - User bubble: transparent bg, neutral Pewter border, only the
+        //   bottom-right corner clipped (the "from-me" tail).
+        // - Assistant bubble: card surface, 2px accent left edge (the
+        //   "illuminated capital"), accent-tinted glow shadow + depth
+        //   shadow, only the bottom-left corner clipped.
         decoration: isUser
             ? BoxDecoration(
                 color: Colors.transparent,
-                border: Border.all(
-                  color: scheme.primary.withValues(alpha: 0.35),
-                  width: 1,
-                ),
+                border: Border.all(color: scheme.outline, width: 1),
                 borderRadius: const BorderRadius.only(
                   topLeft: Radius.circular(16),
                   topRight: Radius.circular(16),
@@ -56,16 +59,28 @@ class ChatMessageBubble extends ConsumerWidget {
                 ),
               )
             : BoxDecoration(
-                color: scheme.surfaceContainerHighest,
+                color: scheme.surface,
                 border: Border(
                   left: BorderSide(color: scheme.primary, width: 2),
                 ),
                 borderRadius: const BorderRadius.only(
-                  topLeft: Radius.circular(4),
+                  topLeft: Radius.circular(16),
                   topRight: Radius.circular(16),
                   bottomLeft: Radius.circular(4),
                   bottomRight: Radius.circular(16),
                 ),
+                boxShadow: [
+                  BoxShadow(
+                    color: scheme.primary.withValues(alpha: 0.14),
+                    blurRadius: 28,
+                    offset: const Offset(0, 4),
+                  ),
+                  BoxShadow(
+                    color: Colors.black.withValues(alpha: 0.4),
+                    blurRadius: 8,
+                    offset: const Offset(0, 2),
+                  ),
+                ],
               ),
         child: Padding(
           padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),