feat: add database schema with WAL mode and FTS5 triggers

SQLite database layer with thread-local connections, WAL journal mode,
foreign key enforcement, and FTS5 full-text search on utterances via
content-table triggers. TDD: 5 tests written first, all passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/shared/database.py

@@ -0,0 +1,88 @@
+import sqlite3
+import threading
+from pathlib import Path
+from app.shared.config import Settings
+
+_local = threading.local()
+
+
+def get_db(settings: Settings) -> sqlite3.Connection:
+    if not hasattr(_local, "conn") or _local.conn is None:
+        conn = sqlite3.connect(settings.db_path, check_same_thread=False)
+        conn.row_factory = sqlite3.Row
+        conn.execute("PRAGMA journal_mode=WAL")
+        conn.execute("PRAGMA foreign_keys=ON")
+        _local.conn = conn
+    return _local.conn
+
+
+def init_schema(settings: Settings) -> None:
+    Path(settings.clips_dir).mkdir(parents=True, exist_ok=True)
+    db = get_db(settings)
+    db.executescript("""
+        CREATE TABLE IF NOT EXISTS rooms (
+            id          INTEGER PRIMARY KEY,
+            name        TEXT NOT NULL UNIQUE,
+            device_label TEXT,
+            is_active   BOOLEAN DEFAULT 0,
+            last_seen   DATETIME,
+            created_at  DATETIME DEFAULT CURRENT_TIMESTAMP
+        );
+
+        CREATE TABLE IF NOT EXISTS speakers (
+            id          INTEGER PRIMARY KEY,
+            name        TEXT NOT NULL,
+            created_at  DATETIME DEFAULT CURRENT_TIMESTAMP,
+            updated_at  DATETIME DEFAULT CURRENT_TIMESTAMP
+        );
+
+        CREATE TABLE IF NOT EXISTS voice_embeddings (
+            id          INTEGER PRIMARY KEY,
+            speaker_id  INTEGER NOT NULL REFERENCES speakers(id) ON DELETE CASCADE,
+            embedding   BLOB NOT NULL,
+            audio_sample BLOB,
+            created_at  DATETIME DEFAULT CURRENT_TIMESTAMP
+        );
+
+        CREATE TABLE IF NOT EXISTS utterances (
+            id                INTEGER PRIMARY KEY,
+            room_id           INTEGER NOT NULL REFERENCES rooms(id),
+            speaker_id        INTEGER REFERENCES speakers(id),
+            transcript        TEXT NOT NULL,
+            embedding         BLOB,
+            match_status      TEXT NOT NULL DEFAULT 'unreviewed',
+            match_confidence  REAL,
+            start_time        DATETIME NOT NULL,
+            end_time          DATETIME NOT NULL,
+            audio_clip_path   TEXT,
+            livekit_room      TEXT,
+            created_at        DATETIME DEFAULT CURRENT_TIMESTAMP
+        );
+
+        CREATE VIRTUAL TABLE IF NOT EXISTS utterances_fts USING fts5(
+            transcript, content=utterances, content_rowid=id
+        );
+
+        CREATE TRIGGER IF NOT EXISTS utterances_ai AFTER INSERT ON utterances BEGIN
+            INSERT INTO utterances_fts(rowid, transcript) VALUES (new.id, new.transcript);
+        END;
+
+        CREATE TRIGGER IF NOT EXISTS utterances_au AFTER UPDATE OF transcript ON utterances BEGIN
+            INSERT INTO utterances_fts(utterances_fts, rowid, transcript)
+                VALUES ('delete', old.id, old.transcript);
+            INSERT INTO utterances_fts(rowid, transcript) VALUES (new.id, new.transcript);
+        END;
+
+        CREATE TRIGGER IF NOT EXISTS utterances_ad AFTER DELETE ON utterances BEGIN
+            INSERT INTO utterances_fts(utterances_fts, rowid, transcript)
+                VALUES ('delete', old.id, old.transcript);
+        END;
+
+        CREATE TABLE IF NOT EXISTS daily_summaries (
+            id            INTEGER PRIMARY KEY,
+            date          DATE NOT NULL UNIQUE,
+            summary_text  TEXT NOT NULL,
+            generated_at  DATETIME DEFAULT CURRENT_TIMESTAMP
+        );
+    """)
+    db.commit()