Filter plugin install suggestions by installed apps (#24996)

## Summary

- Keep the original `TOOL_SUGGEST_DISCOVERABLE_PLUGIN_ALLOWLIST` as a
fallback seed list, so users with no installed plugins still get initial
install suggestions.
- Allow additional install suggestions from trusted marketplaces:
`openai-curated` and `openai-bundled`.
- Require non-fallback, non-configured marketplace candidates to share
`.app.json` connector IDs with already installed plugins.
- Preserve explicit configured plugin discoverables as an override,
while still omitting installed, disabled, and `NOT_AVAILABLE` plugins.

## Context

`list_available_plugins_to_install` controls which plugins the model can
trigger via `request_plugin_install`. We want a small starter set for
empty/new users, but we also want installed workflow plugins to unlock
relevant source plugins without maintaining every source plugin ID by
hand.

This keeps the legacy plugin ID allowlist only as the starter fallback.
For everything else, the trusted marketplace is the candidate boundary,
and installed app connector overlap is the relevance filter. For
example, an installed Sales plugin can make HubSpot and Granola
suggestible when those source plugins are in `openai-curated` and share
Sales app connector IDs, while an unrelated test-source plugin with an
app connector not declared by Sales stays hidden.

## Test Coverage

- Empty/no-installed-plugin case: returns the fallback seed plugins from
the original allowlist.
- Installed-app expansion: returns non-fallback marketplace plugins only
when their app connector IDs overlap with an installed plugin.
- Sales workflow case: installed Sales declares HubSpot and Granola
apps, so `hubspot@openai-curated` and `granola@openai-curated` are
returned.
- Sales negative case: `test-source@openai-curated` has an app connector
not declared by Sales, so it is not returned.
- Existing guardrails: installed plugins, disabled suggestions, and
`NOT_AVAILABLE` plugins remain omitted; explicit configured
discoverables still work as an override.

## Validation

- `just fmt`
- `just test -p codex-core plugins::discoverable::tests`
- `just test -p codex-core` was attempted earlier, but current `main` /
local env failed with unrelated existing failures around missing
`test_stdio_server`, CLI/code-mode MCP tool setup, and
unified_exec/shell snapshot flakes/timeouts. The touched discoverable
tests pass.

codex-rs/core/src/session/turn.rs

@@ -1071,12 +1071,18 @@ pub(crate) async fn built_tools(
         None
     };
     let auth = sess.services.auth_manager.auth().await;
+    let loaded_plugin_app_connector_ids = loaded_plugins
+        .effective_apps()
+        .into_iter()
+        .map(|connector_id| connector_id.0)
+        .collect::<Vec<_>>();
     let discoverable_tools = if apps_enabled && tool_suggest_enabled(turn_context) {
         if let Some(accessible_connectors) = accessible_connectors_with_enabled_state.as_ref() {
             match connectors::list_tool_suggest_discoverable_tools_with_auth(
                 &turn_context.config,
                 auth.as_ref(),
                 accessible_connectors.as_slice(),
+                &loaded_plugin_app_connector_ids,
             )
             .await
             .map(|discoverable_tools| {