feat(memory): missions remember their verdicts, per repository

Until now missions wrote no memory. The chat path records every turn into
the claw's .brain, but a mission's crew is minted per mission, so a brain
keyed by agent would be written once and never read. What persists across
missions is the repository: mission_memory keeps one .brain per repo_id,
writes each judge verdict into it (reason when met, sanitized guidance when
not — the operator reason may quote the acceptance text), and recalls
against the next phase's task text into the brief, under a heading all
three executors carry because it rides on the task.

Recall is BM25 over the keyword index, no embedder; the harness asserts the
brief carries the section once the repo has one judged mission behind it,
and says 'first mission' rather than failing before that. OpenClaw's
flush-before-compaction was the other half of this item and is moot here:
the chat loop has no compaction and already remembers both halves of
every turn.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01WZb5A2kfVfjpdwSochkuHz

crates/cm-api/src/lib.rs

@@ -29,6 +29,7 @@ pub mod mission_delivery;
 pub mod podcast;
 pub mod mission_events;
 pub mod mission_fs;
+pub mod mission_memory;
 pub mod mission_gc;
 pub mod mission_orchestrator;
 pub mod mission_schedule;