fix: address PR #332 review feedback

Addresses 12 of 13 review comments from Copilot and CodeRabbit on
PR #332. One comment (no-manifests in validate-plugins.yml) is
declined and answered inline; the rest are applied here.

Substantive fixes:

- .github/workflows/validate-plugins.yml — add --noconftest to the
  schema-tests step. tests/conftest.py imports structlog at module
  level, but the CI job only installs requirements-test.txt
  (pytest/httpx/jsonschema), so pytest collection would fail at
  conftest import. The schema tests don't use shared fixtures, so
  skipping conftest is safe and avoids dragging the full runtime
  requirements into a 2 KB validation job. (Copilot)

- schema/plugin.schema.json — tighten the server_files regex on both
  settings.server_files and diagnostics.server_files to match the
  runtime _validate_relpath rules in plugins/__init__.py. The
  previous regex only blocked absolute paths, drive letters,
  backslashes, and "..". The runtime also rejects "//", "./",
  "/./", and leading-dotfile segments. Schema-valid manifests are
  now also load-time-valid. Verified the regex against 12 cases:
  the 3 in-tree manifests still validate. (Copilot)

- .claude/skills/plugin-validate/SKILL.md — add a per-iteration
  plugin_ok flag so we no longer print "OK <path>" after an earlier
  FAIL in the same manifest. Schema-pass + id-mismatch previously
  produced both FAIL and OK lines for one plugin. (CodeRabbit)

- docs/websocket-protocol.md — clarify song_info.tuning array length
  is source-dependent (typically 6 guitar, 4 bass, but extended-range
  GP imports can be 7/8/5/6). Recommend highway.getStringCount() for
  the authoritative count. Line 30 already said this; the table row
  on line 12 was the stale half. (CodeRabbit)

Trivial fixes:

- .claude/rules/plugin-author.md — "wants included" -> "wants to
  include" in the settings.server_files rule. (CodeRabbit)

- Markdown MD040 — add `text` language tags to 7 bare-fence code
  blocks across AGENTS.md, docs/PLUGIN_AUTHORING.md,
  docs/testing-plugins.md, docs/plugin-logging.md, .claude/README.md,
  .claude/agents/slopsmith-reviewer.md, and
  .claude/skills/plugin-validate/SKILL.md (two fences). (CodeRabbit)

Declined:

- .github/workflows/validate-plugins.yml no-manifests -> exit 0
  (CodeRabbit suggested exit 1). Plugins in this repo are in-tree,
  not submodules (no .gitmodules, git submodule status empty), and
  the workflow has a path filter on plugins/**/plugin.json so it
  only runs when a manifest actually changes. Exit 0 is correct.
  Answered inline on the PR.

Verification:
  pytest tests/test_plugin_schema.py -v --noconftest    # 8 passed
  python -c "import json,glob,jsonschema; s=json.load(open('schema/plugin.schema.json')); [jsonschema.validate(json.load(open(p)), s) for p in sorted(glob.glob('plugins/*/plugin.json'))]"
  # ok — all 3 in-tree manifests validate against tightened schema
Signed-off-by: Miguel_LZPF <mgcdreamer@gmail.com>

docs/PLUGIN_AUTHORING.md

@@ -6,7 +6,7 @@ This guide is the entry point. Each topic below has a dedicated doc — read wha
 
 ## Quickstart
 
-```
+```text
 plugins/my_plugin/
 ├── plugin.json          Manifest (required) — see docs/plugin-manifest.md
 ├── screen.html          Optional — markup mounted at #plugin-my_plugin

docs/plugin-logging.md

@@ -44,7 +44,7 @@ That logger inherits from the root `slopsmith` logger, which is configured by `l
 
 Look for your plugin's logger name in the console output:
 
-```
+```text
 INFO     slopsmith.plugin.my_plugin: plugin ready
 ```
 

docs/testing-plugins.md

@@ -4,7 +4,7 @@ Slopsmith has three test surfaces — Python unit/integration tests (pytest), JS
 
 ## Test layout
 
-```
+```text
 tests/
 ├── conftest.py          Shared pytest fixtures (isolate_logging)
 ├── test_plugins.py      Plugin loader + load_sibling + collision tests (includes reset_plugin_state)

docs/websocket-protocol.md

@@ -9,7 +9,7 @@ Each connection receives the following JSON frames, roughly in this order:
 | Message | Shape | Description |
 |---------|-------|-------------|
 | `loading` | `{ type: 'loading', stage }` | Status/progress message during extraction or conversion. |
-| `song_info` | `{ type, title, artist, arrangement, arrangement_index, arrangements, duration, tuning, capo, format, audio_url, audio_error, stems }` | Song metadata. `arrangements` is the full list for the switcher. `audio_url` is `null` when audio is unavailable, in which case `audio_error` is non-null; otherwise `audio_error` is `null`. `stems` is always present — an empty array for non-sloppak songs or sloppak songs with no split stems. `tuning` is an array (6 for guitar, 4 for bass). |
+| `song_info` | `{ type, title, artist, arrangement, arrangement_index, arrangements, duration, tuning, capo, format, audio_url, audio_error, stems }` | Song metadata. `arrangements` is the full list for the switcher. `audio_url` is `null` when audio is unavailable, in which case `audio_error` is non-null; otherwise `audio_error` is `null`. `stems` is always present — an empty array for non-sloppak songs or sloppak songs with no split stems. `tuning` is an array whose length depends on the source arrangement (typically 6 for guitar, 4 for bass, but extended-range GP imports can be 7/8 for guitar or 5/6 for bass — use `highway.getStringCount()` for the authoritative count). |
 | `beats` | `{ type, data: [{ time, measure }] }` | Beat timestamps with measure numbers. |
 | `sections` | `{ type, data: [{ time, name }] }` | Named sections (Intro, Verse, Chorus, etc.). |
 | `anchors` | `{ type, data: [{ time, fret, width }] }` | Fret zoom anchors. |