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>

agents/the-scribe.md

@@ -25,7 +25,7 @@ already captured into `raw/` (a PDF, an image) at the absolute path
 ## MCP tools
 
 Read:
-- `graph_summary` — counts, types, tags, most-linked notes.
+- `graph_summary` — counts, repo scopes, the tag vocabulary (`by_tag`), most-linked notes.
 - `graph_search_nodes` — find notes by tag / type / repo / id / free text.
 - `graph_neighbors` — inbound + outbound links of a node, with edge `type` and `annotation`.
 - `read_note` — the Markdown of a note (by `id` or vault-relative `path`). On a