feat: answer /mcp in chat with the MCP server status and a reconnect (#1218)

## Summary

In an ACP client, `/mcp` showed the CLI text "… Use `/mcp` in the
terminal for details." The user of an ACP client has no terminal. In SDK
mode, Claude Code also refuses `/mcp reconnect|enable|disable` with
"Reconnect, enable, and disable aren't available in this session." and
changes nothing.

- `/mcp` and `/mcp reconnect|enable|disable [<server>|all]` still run as
a normal Claude Code turn. The adapter replaces the text of the local
command, through the same hook that `/usage` uses. Prompt order, cancel,
and the provider update stay with the turn.
- For an action, the adapter runs it in that turn through the SDK
control API (`reconnectMcpServer`, `toggleMcpServer`). It shows one
result line for each server, then the status list.
- The status list comes from `query.mcpServerStatus()`. It has a summary
line and groups by status: failed, needs authentication, connecting,
connected, and disabled on one line. A failed server shows a short
cleaned error. A list is used and not a table, because a table breaks
words in narrow columns.
- Useful CLI sentences stay, for example "There's no MCP server named
…". Sentences that point to the terminal are removed.
- After an explicit reconnect, a server from the ACP session that needs
authentication starts the existing MCP OAuth flow, when the client
supports URL elicitation.
- `/mcp` is advertised with the input hint `[reconnect|enable|disable
[<server>|all]]` and is hidden on history replay.

## Other commits in this branch

This branch also carries commits of other work: skill command metadata
for AIR, a faster `session/load` replay, and the resumed permission
mode. They can move to separate PRs if preferred.

## Tests

- `src/tests/mcp-command.test.ts` (61 tests). The fake CLI answers with
the real SDK-mode texts and message shapes (synthetic assistant +
result) and does not change any status.
- A live run through the adapter with a broken and a working stdio
server: `/mcp`, `/mcp disable good`, `/mcp enable good`, `/mcp reconnect
broken`, `/mcp reconnect nosuch`.
- `compare.ts` allows one new difference against the origin/main
baseline: the `mcp` command in `available_commands_update`. The baseline
files are unchanged.
- `npm run check` and `npm run test:run` pass.

README.md

@@ -17,6 +17,7 @@ This tool implements an ACP agent by using the official [Claude Agent SDK](https
 - Interactive (and background) terminals
 - Custom [Slash commands](https://docs.anthropic.com/en/docs/claude-code/slash-commands)
 - Client MCP servers
+- `/mcp` in the chat: the MCP server status as a list. The adapter runs `/mcp reconnect`, `/mcp enable`, and `/mcp disable` through the SDK control API, because Claude Code refuses them in SDK mode. A reconnect of an ACP server that needs authentication starts MCP OAuth through URL elicitation
 - Session-scoped long-running goals for AIR through the [goal extension](docs/air-extensions.md#goal) under `_meta.jetbrains.air.goal`
 - Structured errors, recovery, and warnings through the opt-in [session failure extension](docs/air-extensions.md#session-failure)
 - Concrete model and effort defaults through the opt-in [recommended config value extension](docs/air-extensions.md#recommended-config-values)