feat: wire extension tool bundles into core (#22147)

## Why

This is the next narrow step toward moving concrete tool families out of
core. After #22138 introduced `codex-tool-api`, we still needed a real
end-to-end seam that lets an extension own an executable tool definition
once and have core install it without the temporary `extension-api`
wrapper or a dependency on `codex-tools`.

`codex-tool-api` is the small extension-facing execution contract, while
`codex-tools` still has a different job: host-side shared tool metadata
and planning logic that is not “run this contributed tool”, like spec
shaping, namespaces, discovery, code-mode augmentation, and
MCP/dynamic-to-Responses API conversion

## What changed

- Moved the shared leaf tool-spec and JSON Schema types into
`codex-tool-api`, so the executable contract now lives with
[`ToolBundle`](https://github.com/openai/codex/blob/c538758095337d4fe0a52a172363ccede4066bda/codex-rs/tool-api/src/bundle.rs#L19-L70).
- Replaced the temporary extension-side tool wrapper with direct
`ToolBundle` use in `codex-extension-api`.
- Taught core to collect contributed bundles, include them in spec
planning, register them through
[`ToolRegistryBuilder::register_tool_bundle`](https://github.com/openai/codex/blob/c538758095337d4fe0a52a172363ccede4066bda/codex-rs/core/src/tools/registry.rs#L653-L667),
and dispatch them through the existing router/runtime path.
- Added focused coverage for contributed tools becoming model-visible
and dispatchable, plus spec-planning coverage for contributed function
and freeform tools.

## Verification

- Added `extension_tool_bundles_are_model_visible_and_dispatchable` in
`core/src/tools/router_tests.rs`.
- Added spec-plan coverage in `core/src/tools/spec_plan_tests.rs` for
contributed extension bundles.

## Related

- Follow-up to #22138

codex-rs/Cargo.lock

@@ -2525,6 +2525,7 @@ dependencies = [
  "codex-terminal-detection",
  "codex-test-binary-support",
  "codex-thread-store",
+ "codex-tool-api",
  "codex-tools",
  "codex-utils-absolute-path",
  "codex-utils-cache",
@@ -2825,9 +2826,7 @@ name = "codex-extension-api"
 version = "0.0.0"
 dependencies = [
  "codex-protocol",
- "codex-tools",
- "serde_json",
- "thiserror 2.0.18",
+ "codex-tool-api",
 ]
 
 [[package]]
@@ -3710,10 +3709,7 @@ dependencies = [
 name = "codex-tool-api"
 version = "0.0.0"
 dependencies = [
- "codex-protocol",
- "codex-tools",
  "pretty_assertions",
- "serde",
  "serde_json",
  "thiserror 2.0.18",
 ]