notes: add per-note checklist (to-do list) option

Task #420 — answers the user request "وين خيار اضيف list to do?".

Schema (lib/db/src/schema/notes.ts):
- notes + note_recipients gain `kind` (varchar(16) default 'text')
  and `items` (jsonb<ChecklistItem[]> nullable). Snapshot copy on
  note_recipients keeps delivered checklists immutable across sender
  edits/deletes.
- Drizzle push applied; lib/db .d.ts rebuilt.

API (artifacts/api-server/src/routes/notes.ts):
- ChecklistItem type + bounded parser (≤200 items, id ≤64, text ≤500).
- parseNoteInput normalizes items↔kind on create and on PATCH that
  carries `kind`; PATCH handler additionally coerces items-only
  patches against the note's existing kind so a text note can never
  end up with checklist items (and vice versa).
- POST/PATCH/send/loadRecipientsForNote/received/thread responses and
  the realtime `note_received` payload all carry kind+items, with the
  thread response falling back to the recipient snapshot.

Client (artifacts/tx-os/src/lib/notes-api.ts + pages/notes.tsx):
- Note/ReceivedNote/NoteThread/SentNoteRecipient extended with
  kind+items.
- New `ChecklistEditor`, `ChecklistView`, and `KindToggle` components.
- Composer and EditNoteDialog gain the to-do toggle (ListTodo icon)
  and switch between Textarea and ChecklistEditor; saves send
  kind+items, with empty-checklist auto-discard mirroring the existing
  empty-text behaviour.
- NoteCard, inbox list, sent list, and ThreadDialog body render the
  checklist (read-only on snapshots; owner cards can toggle done via
  PATCH with stopPropagation so the edit dialog doesn't open).

i18n: notes.checklist.{toggle,addItem,itemPlaceholder,emptyHint,
removeItem,progress} added to en.json + ar.json.

Tests: new artifacts/tx-os/tests/notes-checklist.spec.mjs covers
composer→persist→reload→toggle, items-only PATCH normalization on
both kinds, and checklist delivery to recipient snapshot. All 3 pass.

Architect review (evaluate_task) flagged one real issue: items-only
PATCH normalization. Fixed in the PATCH handler and locked in by the
new normalization test.

Pre-existing executive-meetings.ts tsc errors are unchanged and
unrelated to this task.

lib/db/src/schema/notes.ts

@@ -1,4 +1,4 @@
-import { pgTable, text, serial, timestamp, integer, varchar, boolean, primaryKey, uniqueIndex } from "drizzle-orm/pg-core";
+import { pgTable, text, serial, timestamp, integer, varchar, boolean, jsonb, primaryKey, uniqueIndex } from "drizzle-orm/pg-core";
 import { createInsertSchema } from "drizzle-zod";
 import { z } from "zod/v4";
 import { usersTable } from "./users";
@@ -13,6 +13,8 @@ export const noteFoldersTable = pgTable("note_folders", {
   userNameUnique: uniqueIndex("note_folders_user_name_unique").on(t.userId, t.name),
 }));
 
+export type ChecklistItem = { id: string; text: string; done: boolean };
+
 export const notesTable = pgTable("notes", {
   id: serial("id").primaryKey(),
   userId: integer("user_id").notNull().references(() => usersTable.id, { onDelete: "cascade" }),
@@ -20,6 +22,10 @@ export const notesTable = pgTable("notes", {
   title: varchar("title", { length: 300 }).notNull().default(""),
   content: text("content").notNull().default(""),
   color: varchar("color", { length: 32 }).notNull().default("default"),
+  // "text" (plain note) or "checklist" (per-note to-do list). Items live in
+  // `items` for checklist notes; for text notes `items` is null.
+  kind: varchar("kind", { length: 16 }).notNull().default("text"),
+  items: jsonb("items").$type<ChecklistItem[]>(),
   isPinned: boolean("is_pinned").notNull().default(false),
   isArchived: boolean("is_archived").notNull().default(false),
   createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
@@ -65,6 +71,10 @@ export const noteRecipientsTable = pgTable("note_recipients", {
   title: varchar("title", { length: 300 }).notNull().default(""),
   content: text("content").notNull().default(""),
   color: varchar("color", { length: 32 }).notNull().default("default"),
+  // Snapshot of the source note's kind/items at send time so checklist
+  // notes survive (and stay independent of) sender edits/deletes.
+  kind: varchar("kind", { length: 16 }).notNull().default("text"),
+  items: jsonb("items").$type<ChecklistItem[]>(),
   status: varchar("status", { length: 16 }).notNull().default("unread"),
   sentAt: timestamp("sent_at", { withTimezone: true }).notNull().defaultNow(),
   readAt: timestamp("read_at", { withTimezone: true }),