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.

.github/workflows/e2e.yml

@@ -23,7 +23,7 @@ name: E2E (real DeepSeek API)
 # in the BASE repo's context WITH secrets while still able to check out untrusted
 # fork code — a textbook key-leak vector, especially once this repo is public.
 # The fork/secret model and its public-repo implications are recorded in
-# docs/rfc/implemented/2026-06-19-real-api-e2e-ci.md.
+# docs/rfc/implemented/testing/2026-06-19-real-api-e2e-ci.md.
 #
 # Note: scheduled triggers are auto-disabled after 60 days of repo inactivity;
 # push/pull_request/workflow_dispatch act as backstops.