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.

apps/aether-gateway/src/handlers/admin/provider/pool/runtime/keys.rs

@@ -1,4 +1,4 @@
-use aether_data::redis::RedisKeyspace;
+use aether_data::driver::redis::RedisKeyspace;
 
 pub(super) fn pool_sticky_pattern(keyspace: &RedisKeyspace, provider_id: &str) -> String {
     keyspace.key(&format!("ap:{provider_id}:sticky:*"))

apps/aether-gateway/src/handlers/admin/provider/pool/runtime/reads.rs

@@ -7,7 +7,7 @@ use crate::handlers::admin::provider::shared::support::{
     AdminProviderPoolConfig, AdminProviderPoolRuntimeState, ADMIN_PROVIDER_POOL_SCAN_BATCH,
 };
 use crate::GatewayError;
-use aether_data::redis::RedisKvRunner;
+use aether_data::driver::redis::RedisKvRunner;
 use std::collections::BTreeMap;
 use std::time::{SystemTime, UNIX_EPOCH};
 use tracing::warn;

apps/aether-gateway/src/handlers/admin/provider/pool/runtime/writes.rs

@@ -5,7 +5,7 @@ use super::keys::{
 use crate::handlers::admin::provider::shared::support::{
     AdminProviderPoolConfig, AdminProviderPoolUnschedulableRule,
 };
-use aether_data::redis::RedisKvRunner;
+use aether_data::driver::redis::RedisKvRunner;
 use regex::Regex;
 use std::collections::BTreeMap;
 use std::time::{SystemTime, UNIX_EPOCH};