A-3: Unbounded readline() wait -- no timeout on MCP calls

[tcconnally]

lines 237-252

_mcp_send blocks indefinitely waiting for matching response id. A wedged Mimir (e.g. via A-1, or long FTS query) blocks Anna's entire plugin loop with no deadline.

Impact: MEDIUM -- one slow/stuck call freezes all memory tools.

Fix: Read with deadline (selectors on POSIX, reader thread + queue timeout for portability).

[tcconnally]

Fixed by PR #6: Mimir subprocess calls now have readline timeout and proper deadline handling.