Add multi-database data layer

Introduce aether-data-schema and driver-specific schema generation for Postgres, MySQL, and SQLite.

Split data backends, lifecycle, repositories, and gateway runtime integration across database drivers.

Verified with cargo fmt --all --check, cargo clippy --workspace --all-targets -- -D warnings, and cargo test --workspace.

crates/aether-data/schema/drivers/sqlite/baseline/001_identity.sql

@@ -0,0 +1,117 @@
+CREATE TABLE IF NOT EXISTS users (
+    id TEXT PRIMARY KEY,
+    external_id TEXT,
+    email TEXT UNIQUE,
+    username TEXT UNIQUE,
+    password_hash TEXT,
+    role TEXT,
+    auth_source TEXT NOT NULL DEFAULT 'local',
+    email_verified INTEGER NOT NULL DEFAULT 0,
+    is_active INTEGER NOT NULL DEFAULT 1,
+    is_deleted INTEGER NOT NULL DEFAULT 0,
+    allowed_models TEXT,
+    allowed_providers TEXT,
+    allowed_api_formats TEXT,
+    model_capability_settings TEXT,
+    rate_limit INTEGER,
+    metadata TEXT,
+    created_at INTEGER NOT NULL,
+    updated_at INTEGER NOT NULL,
+    last_login_at INTEGER
+);
+
+CREATE TABLE IF NOT EXISTS api_keys (
+    id TEXT PRIMARY KEY,
+    user_id TEXT NOT NULL,
+    key_hash TEXT NOT NULL UNIQUE,
+    key_encrypted TEXT,
+    name TEXT,
+    key_prefix TEXT,
+    status TEXT NOT NULL DEFAULT 'active',
+    allowed_models TEXT,
+    allowed_providers TEXT,
+    allowed_api_formats TEXT,
+    rate_limit INTEGER DEFAULT 100,
+    concurrent_limit INTEGER,
+    force_capabilities TEXT,
+    is_active INTEGER NOT NULL DEFAULT 1,
+    is_locked INTEGER NOT NULL DEFAULT 0,
+    is_standalone INTEGER NOT NULL DEFAULT 0,
+    auto_delete_on_expiry INTEGER NOT NULL DEFAULT 0,
+    total_requests INTEGER NOT NULL DEFAULT 0,
+    total_tokens INTEGER NOT NULL DEFAULT 0,
+    total_cost_usd REAL NOT NULL DEFAULT 0,
+    metadata TEXT,
+    expires_at INTEGER,
+    last_used_at INTEGER,
+    created_at INTEGER NOT NULL,
+    updated_at INTEGER NOT NULL
+);
+CREATE INDEX IF NOT EXISTS api_keys_user_id_idx ON api_keys (user_id);
+
+CREATE TABLE IF NOT EXISTS audit_logs (
+    id TEXT PRIMARY KEY,
+    event_type TEXT NOT NULL,
+    user_id TEXT,
+    api_key_id TEXT,
+    description TEXT NOT NULL,
+    ip_address TEXT,
+    user_agent TEXT,
+    request_id TEXT,
+    event_metadata TEXT,
+    status_code INTEGER,
+    error_message TEXT,
+    created_at INTEGER NOT NULL
+);
+CREATE INDEX IF NOT EXISTS audit_logs_created_at_idx ON audit_logs (created_at);
+CREATE INDEX IF NOT EXISTS audit_logs_event_type_idx ON audit_logs (event_type);
+CREATE INDEX IF NOT EXISTS audit_logs_request_id_idx ON audit_logs (request_id);
+CREATE INDEX IF NOT EXISTS audit_logs_user_id_idx ON audit_logs (user_id);
+
+CREATE TABLE IF NOT EXISTS announcements (
+    id TEXT PRIMARY KEY,
+    title TEXT NOT NULL,
+    content TEXT NOT NULL,
+    type TEXT NOT NULL DEFAULT 'info',
+    priority INTEGER NOT NULL DEFAULT 0,
+    author_id TEXT,
+    is_active INTEGER NOT NULL DEFAULT 1,
+    is_pinned INTEGER NOT NULL DEFAULT 0,
+    start_time INTEGER,
+    end_time INTEGER,
+    created_at INTEGER NOT NULL,
+    updated_at INTEGER NOT NULL
+);
+CREATE INDEX IF NOT EXISTS announcements_author_id_idx ON announcements (author_id);
+CREATE INDEX IF NOT EXISTS announcements_created_at_idx ON announcements (created_at);
+CREATE INDEX IF NOT EXISTS announcements_is_active_idx ON announcements (is_active);
+
+CREATE TABLE IF NOT EXISTS announcement_reads (
+    id TEXT PRIMARY KEY,
+    user_id TEXT NOT NULL,
+    announcement_id TEXT NOT NULL,
+    read_at INTEGER NOT NULL,
+    UNIQUE (user_id, announcement_id)
+);
+CREATE INDEX IF NOT EXISTS announcement_reads_announcement_id_idx ON announcement_reads (announcement_id);
+CREATE INDEX IF NOT EXISTS announcement_reads_user_id_idx ON announcement_reads (user_id);
+
+CREATE TABLE IF NOT EXISTS management_tokens (
+    id TEXT PRIMARY KEY,
+    user_id TEXT NOT NULL,
+    name TEXT NOT NULL,
+    description TEXT,
+    token_hash TEXT NOT NULL UNIQUE,
+    token_prefix TEXT,
+    allowed_ips TEXT,
+    expires_at INTEGER,
+    last_used_at INTEGER,
+    last_used_ip TEXT,
+    usage_count INTEGER NOT NULL DEFAULT 0,
+    is_active INTEGER NOT NULL DEFAULT 1,
+    created_at INTEGER NOT NULL,
+    updated_at INTEGER NOT NULL,
+    UNIQUE (user_id, name)
+);
+CREATE INDEX IF NOT EXISTS management_tokens_user_id_idx ON management_tokens (user_id);
+