Follow-ups from #912: auto-commit refusal hardening and HOME resolution #917

Follow-ups from the review of #912 (non-blocking), tracked here as one issue:

Auto-commit refusal (runAutoCommit, codex-runtime.ts)

1. taskId in the blocker summary is not sanitized. The mail path validates message ids, but the Flair task loop takes event.refId ?? event.id, and refId is only type-checked. Validate or sanitize it before it reaches the summary or the error.
2. The repository path and a spawn error's message enter the error text unsanitized; only the probe's stderr is sanitized.
3. If publishing the blocker fails, the refusal again ends as a warning and a null PR URL in _runAutoCommitLegacy, after the task was reported complete. Consider failing the task itself.
4. publishEvent has no timeout; a hang blocks the refusal (it still fails closed).
5. The sanitizer leaves non-Cc display controls (U+2028/U+2029, bidi overrides U+202A-U+202E and U+2066-U+2069), and .slice(0, 300) can leave a lone surrogate. Decide whether those belong in the replaced set.
6. Text: the function comment omits the .trim(), and "Remove ANSI CSI escapes" does not cover the 8-bit CSI (U+009B is replaced by a space and its parameter bytes stay as text).
7. The long-stderr test pins the cap only to about 456 characters; an assertion on the exact length would pin 300.
8. No real-Flair test covers the blocker event (the test uses a fake publisher).

HOME resolution (#822)
9. About 30 other files under packages/cli/src still resolve paths with os.homedir(). None is reachable from the runtimes changed here, and none is wrong while nothing changes HOME in-process, but consolidating on homeDir() removes the trap that produced #822.
10. bin/tps.ts builds the runtime's mailDir/extraDirs with homedir() at launch; if in-process HOME changes are supported, those stay on the start-up HOME.
11. The Gemini runtime prepends <HOME>/.tps/bin to the child's PATH, so spawn("gemini") also resolves through it; with a per-task, mutable HOME, resolve gemini before prepending.
12. flair-client.ts defaultFlairKeyPath() still uses homedir() (unreachable from these runtimes, which require flairKeyPath).

Refs #822, #824, #912.