fix: handle missing gh executable

[giscebot]

Fixes gisce#25

Summary

• convert a missing configured gh executable into a CompletedProcess-style failure with exit code 127
• keep GitHub follow-up paths from crashing the worker on FileNotFoundError
• add regression coverage for live mode

Tests

• .venv/bin/pytest -q tests/test_modes_cli.py (10 passed)

Moved from gisce#26 at the request of @ecarreras.

[pilipilisbot]

Approved. I reviewed the linked Sentry issue, the migrated PR context, and the full upstream diff across dispatch, monitor, queue, and tests. The GitHubClient run wrapper preserves the CompletedProcess-style contract and turns a missing configured gh executable into return code 127, so reaction, comment, and follow-up paths can fail closed instead of crashing the worker.

The carried monitor and queue resiliency commits are also consistent with repository operations: release lookup failures remain non-fatal, user-home DB paths are expanded, and missing SQLite parent directories are recreated before reconnecting.

Verification:

• Focused local tests: .venv/bin/pytest -q tests/test_modes_cli.py tests/test_monitor.py tests/test_queue.py -> 41 passed
• Full local suite: .venv/bin/pytest -q -> 159 passed, 1 Starlette/httpx deprecation warning
• GitHub checks: dashboard, pytest 3.11, and pytest 3.12 are passing

[pilipilisbot]

Merge event processed: PR #177 is already merged as b0bdf23, carrying the missing-gh fix from ecc87a0. I rechecked the linked Sentry issue context and reran the focused regression tests locally: .venv/bin/pytest -q tests/test_modes_cli.py tests/test_monitor.py tests/test_queue.py -> 41 passed. No follow-up code changes are needed.