Bound worktree freshness fetch (#927)

[chubes4]

Closes #927

Summary

• Give WorktreeStalenessProbe::fetch() the existing five-second bounded git-probe budget through GitRunner/ProcessRunner.
• Classify git_command_timeout as unverified freshness, preserving the existing fail-closed worktree_freshness_unverified gate and allow_unverified_freshness bypass.
• Surface timeout-specific diagnostics and response fields without producing stale-repository evidence.

Source Evidence

• Source relationship: Bound remote fetch during worktree freshness checks #927 identifies the unbounded pre-create git fetch --quiet origin in WorktreeStalenessProbe; nearby lifecycle freshness probes already use the five-second generic git timeout contract.
• Change kind: Narrow owning-layer timeout propagation and structured failure classification.
• Why this is not broader: Only the freshness fetch receives a timeout. Successful fetches and ordinary fetch failures retain their existing paths; stale commit evidence remains omitted whenever freshness is unverified.

Verification

1. composer install --no-interaction --prefer-dist
2. php tests/process-runner-command-spec.php validates a controlled hanging child is terminated and returns the configured generic timeout envelope.
3. php tests/worktree-staleness-fetch-timeout.php verifies the probe passes its five-second budget to its runner and returns actionable structured timeout data without network access.
4. php tests/worktree-add-lifecycle.php verifies successful fetch and ordinary fetch-failure/allow_unverified_freshness lifecycle behavior.
5. for test in tests/*.php; do php "$test" || exit 1; done was attempted: tests through workspace-safe-cleanup-orchestrator passed, then the unrelated tests/worktree-active-no-signal-scope.php failed because it does not require WorktreeCleanupCandidateClassifier.

Verification capability: Focused deterministic coverage and the lifecycle integration test pass. PHPStan is not installed by this repository lockfile (vendor/bin/phpstan is absent).

Compatibility

No input contract changes. Existing successful and ordinary fetch-failure behavior is retained. Callers opting into unverified freshness additionally receive optional fetch_timed_out and fetch_timeout_seconds fields when the bounded fetch expires.

AI Disclosure

Implemented with OpenAI gpt-5.6-terra through Homeboy/OpenCode.