add models, migrations, and CRUD

Schema mirrors the webapp tasks module's ScheduledEvent + EventCompletion
shape:

- tasks.tasks (NIP-52 kind 31922 cache): (pubkey, d_tag) is the
  parameterized-replaceable key. JSON-encoded participants / categories
  / recurrence columns are decoded on read via _parse_task_row so each
  model can keep clean field validators.
- tasks.completions (kind 31925 cache): unique on
  (task_address, pubkey, occurrence). occurrence is NULL for one-shot
  tasks; create_completion deletes any prior claim for the same triple
  so the latest event wins.
- tasks.settings: singleton row with public_listing toggle.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

migrations.py

@@ -1 +1,76 @@
-# Migrations are filled in by the next commit.
+async def m001_initial(db):
+    """
+    Tasks table (NIP-52 kind 31922 cache) and completions table (kind 31925
+    cache). The (pubkey, d_tag) pair is the parameterized-replaceable key.
+    """
+    await db.execute(
+        f"""
+        CREATE TABLE tasks.tasks (
+            id TEXT PRIMARY KEY,
+            wallet TEXT NOT NULL,
+            pubkey TEXT NOT NULL,
+            d_tag TEXT NOT NULL,
+            title TEXT NOT NULL,
+            start_date TEXT NOT NULL,
+            end_date TEXT,
+            description TEXT NOT NULL DEFAULT '',
+            location TEXT,
+            status TEXT NOT NULL DEFAULT 'pending',
+            event_type TEXT NOT NULL DEFAULT 'task',
+            participants TEXT,
+            categories TEXT,
+            recurrence TEXT,
+            nostr_event_id TEXT,
+            nostr_event_created_at INTEGER,
+            time TIMESTAMP NOT NULL DEFAULT {db.timestamp_now}
+        );
+    """
+    )
+    await db.execute(
+        "CREATE UNIQUE INDEX tasks_pubkey_dtag_idx "
+        "ON tasks.tasks (pubkey, d_tag)"
+    )
+
+    await db.execute(
+        f"""
+        CREATE TABLE tasks.completions (
+            id TEXT PRIMARY KEY,
+            task_address TEXT NOT NULL,
+            pubkey TEXT NOT NULL,
+            occurrence TEXT,
+            task_status TEXT NOT NULL DEFAULT 'claimed',
+            completed_at INTEGER,
+            notes TEXT NOT NULL DEFAULT '',
+            nostr_created_at INTEGER NOT NULL,
+            time TIMESTAMP NOT NULL DEFAULT {db.timestamp_now}
+        );
+    """
+    )
+    # occurrence is NULL for one-shot tasks; the (task_address, pubkey,
+    # occurrence) tuple identifies "the latest claim by this user for this
+    # specific occurrence".
+    await db.execute(
+        "CREATE INDEX tasks_completions_address_idx "
+        "ON tasks.completions (task_address)"
+    )
+    await db.execute(
+        "CREATE INDEX tasks_completions_pubkey_idx "
+        "ON tasks.completions (pubkey)"
+    )
+
+
+async def m002_settings(db):
+    """Singleton settings row for the admin UI."""
+    await db.execute(
+        """
+        CREATE TABLE IF NOT EXISTS tasks.settings (
+            id INTEGER PRIMARY KEY DEFAULT 1,
+            public_listing BOOLEAN NOT NULL DEFAULT FALSE
+        )
+        """
+    )
+    await db.execute(
+        "INSERT INTO tasks.settings (id, public_listing) "
+        "SELECT 1, FALSE WHERE NOT EXISTS "
+        "(SELECT 1 FROM tasks.settings WHERE id = 1)"
+    )