docs: fix broken file references found by path-existence crosscheck

Ran a doc-vs-filesystem crosscheck: extracted every backtick-quoted
path with a file extension or known directory prefix from docs/*.md
and verified each exists. After filtering false positives
(placeholder paths, config keys mistaken for paths, paths inside
docs that already have historical-status banners), found 4 real
broken references — 3 fixed in docs, 1 fixed by creating the missing
file:

docs/HOW_TO_RUN_TESTS.md:339
- Claimed ".github/workflows/tests.yml" exists and runs pytest on
  multiple Python versions in CI. There is no such workflow.
  The only GitHub Actions file is security-audit.yml (bandit + semgrep).
- Pytest runs locally but is NOT gated on PRs.
- Replaced the fictional CI section with the actual state and a
  note explaining how someone could contribute a real test workflow.

docs/MIGRATION_GUIDE.md:92
- Referenced scripts/fix_perms/README.md "(if exists)" — the
  hedge betrays that the writer wasn't sure. The README didn't
  exist. The 6 scripts in scripts/fix_perms/ were never documented.
- Created the missing scripts/fix_perms/README.md from scratch
  with one-line descriptions of all 6 scripts (fix_assets,
  fix_cache, fix_plugin, fix_web, fix_nhl_cache, safe_plugin_rm)
  + when-to-use-each guidance + usage examples.
- Updated MIGRATION_GUIDE link to drop the "(if exists)" hedge
  since the file now exists.

docs/FONT_MANAGER.md:376
- "See test/font_manager_example.py for a complete working example"
  — that file does not exist. Verified by listing test/ directory.
- Replaced with a pointer to src/font_manager.py itself and the
  existing scoreboard base classes in src/base_classes/ that
  actually use the font manager API in production.

Path-existence check methodology:
- Walked docs/ recursively, regex-extracted backtick-quoted paths
  matching either /\.(py|sh|json|yml|yaml|md|txt|service|html|js|css|ttf|bdf|png)/
  or paths starting with known directory prefixes (scripts/, src/,
  config/, web_interface/, systemd/, assets/, docs/, test/, etc.)
- Filtered out URLs, absolute paths (placeholders), and paths
  without slashes (likely not relative refs).
- Checked existence relative to project root.
- Out of 80 unique relative paths in docs/, 32 didn't exist on
  disk. Most were false positives (configkeys mistaken for paths,
  example placeholders like 'assets/myfont.ttf', historical
  references inside docs that already have status banners). The 4
  above were genuine broken refs.

This pattern is reusable for future iterations and worth wiring
into CI (link checker like lychee, scoped to fenced code paths
rather than just markdown links, would catch the same class).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/HOW_TO_RUN_TESTS.md

@@ -336,11 +336,15 @@ pytest --cov=src --cov-report=html
 
 ## Continuous Integration
 
-Tests are configured to run automatically in CI/CD. The GitHub Actions workflow (`.github/workflows/tests.yml`) runs:
+There is currently no CI test workflow in this repo — `pytest` runs
+locally but is not gated on PRs. The only GitHub Actions workflow is
+[`.github/workflows/security-audit.yml`](../.github/workflows/security-audit.yml),
+which runs bandit and semgrep on every push.
 
-- All tests on multiple Python versions (3.10, 3.11, 3.12)
-- Coverage reporting
-- Uploads coverage to Codecov (if configured)
+If you'd like to add a test workflow, the recommended setup is a
+`.github/workflows/tests.yml` that runs `pytest` against the
+supported Python versions (3.10, 3.11, 3.12, 3.13 per
+`requirements.txt`). Open an issue or PR if you want to contribute it.
 
 ## Best Practices