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/chat/chat_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 '../../core/exceptions.dart';
@@ -173,7 +174,7 @@ class _ChatScreenState extends ConsumerState<ChatScreen>
                     height: 18,
                     child: CircularProgressIndicator(strokeWidth: 2),
                   )
-                : const Icon(Icons.refresh),
+                : const Icon(LucideIcons.refreshCw),
           ),
         ],
       ),
@@ -280,7 +281,7 @@ class _ChatScreenState extends ConsumerState<ChatScreen>
                             child:
                                 CircularProgressIndicator(strokeWidth: 2),
                           )
-                        : const Icon(Icons.send),
+                        : const Icon(LucideIcons.send),
                   ),
                 ],
               ),

lib/screens/chat/conversations_tab_screen.dart

@@ -1,8 +1,10 @@
 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/theme.dart';
 import '../../providers/chat_provider.dart';
 import 'chat_screen.dart';
 
@@ -51,6 +53,9 @@ class _ConversationsTabScreenState
               child: const Text('Cancel')),
           FilledButton(
               onPressed: () => Navigator.pop(dialogContext, true),
+              style: FilledButton.styleFrom(
+                backgroundColor: Theme.of(dialogContext).extension<ActionColors>()!.destructive,
+              ),
               child: const Text('Delete')),
         ],
       ),
@@ -74,7 +79,7 @@ class _ConversationsTabScreenState
         title: Text('Chat', style: theme.textTheme.titleLarge),
         actions: [
           IconButton(
-            icon: const Icon(Icons.add),
+            icon: const Icon(LucideIcons.plus),
             tooltip: 'New conversation',
             onPressed: _createConversation,
           ),
@@ -89,14 +94,14 @@ class _ConversationsTabScreenState
               child: Column(
                 mainAxisSize: MainAxisSize.min,
                 children: [
-                  Icon(Icons.chat_bubble_outline,
+                  Icon(LucideIcons.messageCircle,
                       size: 48, color: theme.colorScheme.onSurfaceVariant),
                   const SizedBox(height: 16),
                   Text('No conversations yet',
                       style: theme.textTheme.titleMedium),
                   const SizedBox(height: 8),
                   FilledButton.icon(
-                    icon: const Icon(Icons.add),
+                    icon: const Icon(LucideIcons.plus),
                     label: const Text('Start a conversation'),
                     onPressed: _createConversation,
                   ),
@@ -113,7 +118,7 @@ class _ConversationsTabScreenState
                 final c = convs[i];
                 final selected = isWide && c.id == _selectedConvId;
                 return ListTile(
-                  leading: const Icon(Icons.chat_bubble_outline),
+                  leading: const Icon(LucideIcons.messageCircle),
                   title: Text(
                       c.title.isEmpty ? 'New conversation' : c.title,
                       maxLines: 1,
@@ -124,7 +129,7 @@ class _ConversationsTabScreenState
                   ),
                   selected: selected,
                   trailing: IconButton(
-                    icon: const Icon(Icons.delete_outline),
+                    icon: const Icon(LucideIcons.trash2),
                     onPressed: () => _confirmDelete(c.id, c.title),
                   ),
                   onTap: () => _openConversation(c.id),
@@ -155,7 +160,7 @@ class _ConversationsTabScreenState
                   child: Column(
                     mainAxisSize: MainAxisSize.min,
                     children: [
-                      Icon(Icons.chat_bubble_outline,
+                      Icon(LucideIcons.messageCircle,
                           size: 48,
                           color: theme.colorScheme.onSurfaceVariant),
                       const SizedBox(height: 16),