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/tasks/task_edit_screen.dart

@@ -1,9 +1,11 @@
 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';
 
 import '../../core/constants.dart';
 import '../../core/exceptions.dart';
+import '../../core/theme.dart';
 import '../../data/models/task.dart';
 import '../../providers/api_client_provider.dart';
 import '../../providers/tasks_provider.dart';
@@ -111,6 +113,9 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
               child: const Text('Cancel')),
           TextButton(
               onPressed: () => Navigator.pop(dialogContext, true),
+              style: TextButton.styleFrom(
+                foregroundColor: Theme.of(dialogContext).extension<ActionColors>()!.destructive,
+              ),
               child: const Text('Delete')),
         ],
       ),
@@ -190,7 +195,7 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
             actions: [
               if (widget.taskId != null)
                 IconButton(
-                  icon: const Icon(Icons.delete),
+                  icon: const Icon(LucideIcons.trash2),
                   onPressed: _delete,
                 ),
               IconButton(
@@ -200,7 +205,7 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
                         height: 20,
                         child: CircularProgressIndicator(strokeWidth: 2),
                       )
-                    : const Icon(Icons.check),
+                    : const Icon(LucideIcons.check),
                 onPressed: _saving ? null : _save,
               ),
             ],
@@ -272,10 +277,10 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
                             title: Text(_dueDate == null
                                 ? 'No due date'
                                 : 'Due: ${_dueDate!.toLocal().toString().substring(0, 10)}'),
-                            leading: const Icon(Icons.calendar_today),
+                            leading: const Icon(LucideIcons.calendarDays),
                             trailing: _dueDate != null
                                 ? IconButton(
-                                    icon: const Icon(Icons.clear),
+                                    icon: const Icon(LucideIcons.x),
                                     onPressed: () =>
                                         setState(() => _dueDate = null),
                                   )
@@ -331,7 +336,7 @@ class _SubTasksSection extends ConsumerWidget {
             const Spacer(),
             TextButton.icon(
               onPressed: onAdd,
-              icon: const Icon(Icons.add, size: 16),
+              icon: const Icon(LucideIcons.plus, size: 16),
               label: const Text('Add'),
               style: TextButton.styleFrom(
                 foregroundColor: colorScheme.primary,