feat: mirror tag-vocabulary summary and note-type validation

Ports two changes from the knowledge-base vault this skeleton is extracted
from, keeping the shared scripts byte-identical across the pair:

- `graph_summary` reports `by_tag` and `tag_count`, sized by `topTags`, and
  drops the `by_type`/`by_status` breakdowns. An MCP-only agent could not
  otherwise discover the tag spellings that `graph_search_nodes` matches
  verbatim.
- `generate-graph.py --validate` now enforces a controlled vocabulary for a
  note's `type`, which is where the drift signal `by_type` used to give now
  lives. `AGENT_QUERY_GUIDE.md`, both skills and the-knowing-one quote the
  enforced enum.

`tests/test_generate_graph.py` is new; `make test` is 50 tests. Regenerating
the graph also drops a stale `GLOBAL_AGENTS` node for a file this skeleton
does not carry.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

skills/knowledge-base-ingest-resource/SKILL.md

@@ -229,7 +229,8 @@ last_reviewed: <today, YYYY-MM-DD>
 
 - `ingested` and `last_reviewed` = today (the `currentDate` from session context).
 - `type` must stay within the vault taxonomy enum
-  (`hub|project|guideline|policy|feature|roadmap|decision|note|meta`) — use `note`;
+  (`hub|project|area|guideline|policy|feature|roadmap|decision|note|meta|reference`),
+  which `generate-graph.py --validate` enforces — use `note`;
   the `resource` tag is what marks it.
 - Markdown link targets resolve by `id`, rel-path, title, or unique stem — always
   use the `id` as the target, e.g. `[Human title](resource/foo/bar)`.

skills/knowledge-base-read/SKILL.md

@@ -29,7 +29,8 @@ README.md                   vault hub; AGENT_QUERY_GUIDE.md   graph query refere
 ```
 
 Every note carries taxonomy frontmatter: `id`, `title`, `type`
-(`hub|project|guideline|policy|feature|roadmap|decision|note|meta`), `status`
+(`hub|project|area|guideline|policy|feature|roadmap|decision|note|meta|reference`, enforced by
+`generate-graph.py --validate`), `status`
 (`active|draft|deprecated`), `tags`, `last_reviewed`, optional `repo`. Notes are
 linked with typed markdown links — `[text](note-id){"type":"…"}` — that resolve
 by `id`. Legacy `[[wiki links]]` are rejected by `make validate-graph`.