🏗️ Extract tome from spire into standalone plugin

Tome is opt-in per project — each project declares its own knowledge
management approach. Spire retains a small knowledge-awareness skill
that explains what tome does and provides a fallback strategy for
projects without it.

- New plugins/tome/ with own manifests, README, all 5 sub-skills
- Spire keeps skills/knowledge/SKILL.md as awareness stub
- Updated all READMEs and marketplace JSONs
- tome: namespace refs now correct (tome is its own plugin)

plugins/tome/skills/check/SKILL.md

@@ -0,0 +1,33 @@
+---
+name: check
+description: >
+  Validate tome knowledge-layer health — broken Markdown links, referenced source paths
+  that no longer exist, missing generated navigation resources, invalid control-file
+  headings or wiki front-matter, and generated folder navigation that has drifted from
+  the current repository structure. Human-triggered; CI-friendly (non-zero exit on
+  error-severity findings).
+disable-model-invocation: true
+allowed-tools: Bash(just:*), Bash(uv run:*)
+---
+
+# Tome — Check
+
+```bash
+just tome check
+```
+
+(Equivalent without the Justfile: `uv run -q --script <tome-plugin-dir>/bin/knowledge.py check`)
+
+Review the findings. `check` validates only **objective, mechanically verifiable**
+issues:
+
+- Broken Markdown links (local targets that do not exist).
+- Referenced source paths (`source-paths`) that no longer exist.
+- Missing generated navigation resources (`boot.md`, wiki nav).
+- Invalid recognized control-file headings / structure.
+- Invalid wiki front-matter `status` values.
+- Generated folder navigation that differs from the current repository structure.
+
+It exits non-zero when there are **error**-severity findings (suitable for CI);
+warnings alone do not fail. Subjective semantic quality and architectural correctness
+are out of scope — that judgment belongs to `/tome:curate` and to humans.