Revert state DB injection and agent graph store (#21481)

## Why

Reverts #20689 to restore the previous optional state DB plumbing. The
conflict resolution keeps the newer installation ID and session/thread
identity changes that landed after #20689, while removing the mandatory
state DB and agent graph store dependency from ThreadManager
construction.

## What changed

- Restored `Option<StateDbHandle>` through app-server, MCP server,
prompt debug, and test entry points.
- Removed the `codex-core` dependency on `codex-agent-graph-store` and
reverted descendant lookup back to the existing state DB path when
available.
- Kept newer `installation_id` forwarding by passing it beside the
optional DB handle.
- Kept local thread-name updates working when the optional state DB
handle is absent.

## Validation

- `git diff --check`
- `cargo test -p codex-thread-store`
- `cargo test -p codex-state -p codex-rollout -p
codex-app-server-protocol`
- Attempted `env CARGO_INCREMENTAL=0 cargo test -p codex-core -p
codex-app-server -p codex-app-server-client -p codex-mcp-server -p
codex-thread-manager-sample -p codex-tui`; blocked locally by a rustc
ICE while compiling `v8 v146.4.0` with `rustc 1.93.0 (254b59607
2026-01-19)` on `aarch64-apple-darwin`.

codex-rs/thread-store/src/local/create_thread.rs

@@ -22,12 +22,12 @@ pub(super) async fn create_thread(
         })?;
     let config = RolloutConfig {
         codex_home: store.config.codex_home.clone(),
-        sqlite_home: store.sqlite_home(),
+        sqlite_home: store.config.sqlite_home.clone(),
         cwd,
         model_provider_id: params.metadata.model_provider.clone(),
         generate_memories: matches!(params.metadata.memory_mode, ThreadMemoryMode::Enabled),
     };
-    let state_db_ctx = Some(store.state_db());
+    let state_db_ctx = store.state_db().await;
     let recorder = RolloutRecorder::new(
         &config,
         RolloutRecorderParams::new(