mark codebase-retrieval as read-only with the MCP readOnlyHint annotation #170

when auggie runs as an MCP server (auggie --mcp), the tools/list response for codebase-retrieval carries no annotations object at all. verified on 0.30.0 and 0.36.0 by sending initialize and tools/list over stdio: the tool comes back with name, description and inputSchema only.

the MCP spec defines tool annotations (readOnlyHint, destructiveHint, idempotentHint, openWorldHint) so a client can tell a read-only tool from one that changes state. some clients use readOnlyHint to decide whether a tool may run without a confirmation prompt while the agent is in a read-only planning mode. without the hint, codebase-retrieval is treated as a possible write, so the client asks for approval before every single retrieval even though the tool only reads the index. allow-list rules on the client side do not override that check, only the annotation does.

please set annotations to { readOnlyHint: true } on codebase-retrieval (and codebase-retrieval-raw where it is exposed) in the tools/list response. idempotentHint true and openWorldHint false would also be accurate for this tool.

to reproduce:

1. run auggie --mcp --mcp-auto-workspace
2. send initialize, notifications/initialized, then tools/list over stdio
3. inspect result.tools[0].annotations, which is undefined

environment: auggie 0.36.0 (commit 7c61e5bb), windows 11, node 26.3.1.