feat(scripts): generate the RFC index tables from the tree

docs/rfc/README.md's per-lifecycle tables are now generated between
gen-rfc-index marker comments from each RFC's path (lifecycle/class),
H1 title (optional 'RFC: ' prefix stripped), and filename date, sorted
by date then filename — the one docs region every proposal wave edits
and every concurrent branch conflicts on becomes derived state.

scripts/rfc-index.ts owns the shared walker (closed lifecycle/class
sets, structure rules, parseable-H1 requirement) and the renderer;
gen-rfc-index.ts is the writer CLI; verify-rfc-classification.ts keeps
the structure check and asserts the committed regions byte-match a
fresh render (freshness subsumes the index-completeness check, since a
generated-from-disk table is definitionally complete and correctly
headed). A malformed H1 is a hard error in both directions, so the H1
is now load-bearing as the title source — the one nonconforming H1
(a status suffix duplicating the path) is normalized.

Implements docs/rfc/implemented/process/2026-07-04-generate-rfc-index-tables.md
(moved from proposed/ and amended to the shipped mechanics); the
classification RFC's verify-only stance carries the supersession
cross-link per implemented/AGENTS.md.

docs/rfc/proposed/feature/2026-06-30-pre-tool-input-rewrite.md

@@ -1,4 +1,4 @@
-# RFC: Pre-tool input rewrite — a consistent design (proposed)
+# RFC: Pre-tool input rewrite — a consistent design
 
 Status: proposed (2026-06-30)