refactor: declarative context-menu registry; named selection threshold

CONTEXT_MENU_ENTRIES maps every menu id to {action, style, parentId,
title}, replacing the split('-') id parsing that only worked because no
name contained a hyphen. Foreign menu ids are now ignored explicitly.
Parity pinned by tests enumerating all 30 previous ids. The 10-char
toolbar trigger threshold is now the named MIN_SELECTION_LENGTH.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/lib/actions.ts

@@ -21,3 +21,43 @@ export type WritingStyle = (typeof WRITING_STYLES)[number];
 
 // Context menus omit 'Default' — the parent action item already covers it.
 export const CONTEXT_MENU_STYLES = WRITING_STYLES.filter((s) => s !== 'Default');
+
+// Minimum selection length (chars, after trim) before the floating toolbar
+// appears. Kept deliberately above 1-2 chars so accidental double-click
+// selections don't trigger the UI.
+export const MIN_SELECTION_LENGTH = 10;
+
+// ─── Context-menu registry ────────────────────────────────────────────────────
+// Declarative id -> {action, style} mapping. Replaces the old split('-')
+// parsing of menuItemId, which only worked because no action or style name
+// contained a hyphen. Order matters: each parent precedes its children so
+// chrome.contextMenus.create never sees an unknown parentId.
+
+export interface ContextMenuEntry {
+  id: string;
+  action: ActionId;
+  style: WritingStyle;
+  // 'Default' entries are top-level parents; styled entries nest under them.
+  parentId?: string;
+  title: string;
+}
+
+export const CONTEXT_MENU_ENTRIES: ContextMenuEntry[] = ACTIONS.flatMap((action) => [
+  {
+    id: `lexai-${action}`,
+    action,
+    style: 'Default' as WritingStyle,
+    title: `⚡ LexAI: ${ACTION_LABELS[action]}`,
+  },
+  ...CONTEXT_MENU_STYLES.map((style) => ({
+    id: `lexai-${action}-${style.toLowerCase()}`,
+    action,
+    style,
+    parentId: `lexai-${action}`,
+    title: style as string,
+  })),
+]);
+
+export function findContextMenuEntry(menuItemId: string): ContextMenuEntry | undefined {
+  return CONTEXT_MENU_ENTRIES.find((e) => e.id === menuItemId);
+}