docs(rfc): classify RFCs by kind via path-encoded subdirectories

Add a second axis to every RFC — its class (feature, bug-fix,
simplification, architecture, process, testing) — encoded in the path
as docs/rfc/{lifecycle}/{class}/file.md. The folder is the label, so
the closed set is enforced by structure rather than a parsed field.

Two new doc-sync gates back it:
- verify-rfc-classification: every RFC sits in a valid class folder and
  the README index lists it under the matching lifecycle→class heading.
- verify-doc-refs: every docs/*.md path cited in a packages|examples TS
  comment resolves — closes a drift class verify-md-links can't see, and
  catches the four comment refs this reorg moved.

The README gains a Classification section explaining the taxonomy and
per-class index sub-sections. A self-referential process RFC records why
the scheme is path-encoded and gated.

packages/session-persistence-sqlite/README.md

@@ -1,6 +1,6 @@
 # @deepseek-ai/dsh-session-persistence-sqlite
 
-A SQLite durable session-persistence backend — a second `SessionPersistence` implementation ([session persistence](../../docs/rfc/implemented/2026-06-14-session-persistence.md)), built to validate that the abstract seam and the shared `runPersistenceContract` suite are genuinely backend-agnostic. It satisfies the SAME contract as `dsh-session-persistence-jsonl` (append-only, contiguous-seq, lazy materialization, interrupted-turn close on load), expressed over `node:sqlite` rows instead of file bytes.
+A SQLite durable session-persistence backend — a second `SessionPersistence` implementation ([session persistence](../../docs/rfc/implemented/architecture/2026-06-14-session-persistence.md)), built to validate that the abstract seam and the shared `runPersistenceContract` suite are genuinely backend-agnostic. It satisfies the SAME contract as `dsh-session-persistence-jsonl` (append-only, contiguous-seq, lazy materialization, interrupted-turn close on load), expressed over `node:sqlite` rows instead of file bytes.
 
 > **TODO:** this backend talks to `node:sqlite` directly. If a cordis database service (`cordis/db` / a `@cordisjs` SQL driver plugin) is adopted, route through that instead of holding a raw `DatabaseSync` here — the contract surface (`SessionPersistence`) would not change, only the storage driver.