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/screens/library/project_tasks_screen.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:lucide_icons/lucide_icons.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
@@ -55,11 +56,11 @@ class _ProjectTasksScreenState extends ConsumerState<ProjectTasksScreen> {
   }
 
   Color _parseColor(String? hex) {
-    if (hex == null || hex.isEmpty) return const Color(0xFF7C3AED);
+    if (hex == null || hex.isEmpty) return const Color(0xFF5B4A8A);
     try {
       return Color(int.parse(hex.replaceFirst('#', '0xFF')));
     } catch (_) {
-      return const Color(0xFF7C3AED);
+      return const Color(0xFF5B4A8A);
     }
   }
 
@@ -96,7 +97,7 @@ class _ProjectTasksScreenState extends ConsumerState<ProjectTasksScreen> {
         ),
         actions: [
           IconButton(
-            icon: const Icon(Icons.edit_outlined),
+            icon: const Icon(LucideIcons.pencil),
             tooltip: 'Edit project',
             onPressed: () =>
                 context.push('/projects/${widget.projectId}/edit'),
@@ -133,7 +134,7 @@ class _ProjectTasksScreenState extends ConsumerState<ProjectTasksScreen> {
         child: Column(
           mainAxisSize: MainAxisSize.min,
           children: [
-            Icon(Icons.check_box_outlined,
+            Icon(LucideIcons.checkSquare,
                 size: 48,
                 color: Theme.of(context).colorScheme.onSurfaceVariant),
             const SizedBox(height: 12),
@@ -302,9 +303,9 @@ class _TaskRow extends StatelessWidget {
   });
 
   IconData get _statusIcon => switch (effectiveStatus) {
-        TaskStatus.done => Icons.check_circle,
-        TaskStatus.inProgress => Icons.timelapse,
-        TaskStatus.todo => Icons.radio_button_unchecked,
+        TaskStatus.done => LucideIcons.checkCircle2,
+        TaskStatus.inProgress => LucideIcons.loader,
+        TaskStatus.todo => LucideIcons.circle,
       };
 
   Color _statusColor(BuildContext context) {