Add a `spawn_history` daemon module backing the spawn form's "recent dirs"
picker. Sidecars are deleted on kill, so they can't be the source — use an
append-only JSONL log at `<state_dir>/spawn-history.jsonl`, one record per
successful spawn (cwd, command, name, worktree_branch, at).
- Write: `SessionManager::create` appends after a successful spawn,
best-effort — a log-write failure only warns, never fails the spawn.
- Read: `recent_dirs()` folds newest-first, dedups by cwd, drops entries past
the recency cap, caps the result count.
- Prune: opportunistic `compact()` from `append` once the file passes a size
threshold; atomic tmp+rename rewrite.
- Config: `[daemon].spawn_history_days` (default 30, `0` disables). History is
wired into the manager at daemon startup.
Time-dependent logic is factored into `*_as_of(now)` helpers for
deterministic unit tests. Adds module unit tests (append/dedup/recency
prune/compaction/disabled/malformed/cap), a config resolution test, and
real-tmux integration tests proving create→append→read end to end.
Closes#24
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>