Add FastAPI app skeleton: settings, db, models, security, auth

- settings.py: pydantic-settings config for the two mount points
  (MUSIC_DATA_DIR, ALEMBIC_CONFIG_DIR), OIDC client config, encryption key path
- db.py: SQLite engine with WAL mode, plain-SQL schema migration runner
  (schema/*.sql, tracked by schema_version -- not the alembic migration tool)
- models.py: SQLAlchemy ORM models matching schema/0001_init.sql
- security/crypto.py: Fernet encrypt/decrypt for the secrets table
- security/oidc.py + routers/auth.py: Pocket ID OIDC login/callback/logout
- security/deps.py: require_auth dependency (redirect-to-login on no session)
- main.py: app factory, lifespan (init_db + beets WAL enable), session
  middleware, minimal dashboard route

Verified boots end-to-end via TestClient: unauthenticated GET / redirects to
/auth/login, static files serve, and all 13 schema tables get created on
first run.

app/static/style.css

@@ -0,0 +1,90 @@
+:root {
+  color-scheme: light dark;
+  --bg: #ffffff;
+  --fg: #1a1a1a;
+  --muted: #666;
+  --border: #ddd;
+  --accent: #2a6f97;
+}
+
+@media (prefers-color-scheme: dark) {
+  :root {
+    --bg: #14161a;
+    --fg: #e8e8e8;
+    --muted: #999;
+    --border: #333;
+    --accent: #6fb3d8;
+  }
+}
+
+* { box-sizing: border-box; }
+
+body {
+  margin: 0;
+  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
+  background: var(--bg);
+  color: var(--fg);
+}
+
+.topbar {
+  display: flex;
+  align-items: center;
+  gap: 1.5rem;
+  padding: 0.75rem 1.25rem;
+  border-bottom: 1px solid var(--border);
+}
+
+.topbar .brand {
+  font-weight: 700;
+  font-size: 1.1rem;
+  color: var(--accent);
+  text-decoration: none;
+}
+
+.topbar nav {
+  display: flex;
+  gap: 1rem;
+  flex: 1;
+}
+
+.topbar a {
+  color: var(--fg);
+  text-decoration: none;
+}
+
+.topbar nav a:hover {
+  color: var(--accent);
+}
+
+.logout {
+  font-size: 0.9rem;
+  color: var(--muted);
+}
+
+main {
+  max-width: 960px;
+  margin: 2rem auto;
+  padding: 0 1.25rem;
+}
+
+.muted { color: var(--muted); }
+
+table {
+  width: 100%;
+  border-collapse: collapse;
+}
+
+th, td {
+  text-align: left;
+  padding: 0.4rem 0.6rem;
+  border-bottom: 1px solid var(--border);
+}
+
+button, .btn {
+  background: var(--accent);
+  color: #fff;
+  border: none;
+  padding: 0.5rem 1rem;
+  border-radius: 4px;
+  cursor: pointer;
+}