docs(rfc): define and enforce a uniform RFC format; adopt it across the corpus

Define the in-file RFC contract in docs/rfc/README.md § The file format:
the header block (`# RFC: <title>` plus a dateless Status enum
cross-checked against the lifecycle folder), the per-lifecycle body
skeleton (a Problem opener everywhere; Proposal/Alternatives considered/
Acceptance criteria/Risks in proposed/; present-tense Decision/
Consequences with proposal-era headings banned in implemented/; the
frozen proposal shape in rejected/), and a mandatory Alternatives
considered section with a date-fenced grandfather comment for pre-format
RFCs whose alternatives are not reconstructible from the record.

Enforce it with a new doc-sync gate, scripts/verify-rfc-format.ts, and
normalize all 112 RFCs to it: ~15 Status-line spellings collapse to the
enum, 29 Context openers become Problem, the 39 legacy-format XXX debt
markers are resolved and banned from reappearing, proposal-era sections
in implemented RFCs are rewritten to shipped reality (including the
web/fs/subagent seam RFCs' migration plans and test checklists, closing
the doc-tiers deferred-work item on the web seam), every RFC gains an
Alternatives considered section or the grandfather comment, and the
bilingual pair is re-mirrored and re-recorded.

Move the generated index tables out of README.md into a fully generated
docs/rfc/INDEX.md — gen-rfc-index now writes the whole file, and
verify-rfc-classification checks its freshness and rejects index-shaped
rows in the curated README — which makes room for the format contract to
live in the README front door instead of a separate FORMAT.md.

The decision record, and the first RFC written in the new format, is
docs/rfc/implemented/process/2026-07-05-uniform-rfc-format.md.

docs/rfc/implemented/testing/2026-06-22-subagent-snapshot-replay.md

@@ -31,6 +31,8 @@ This keys by WHO calls, not by global call order — so it stays correct even if
 
 The ordering key is the session header `createdAt`. In the current synchronous cut this is sound because sibling children are created **strictly sequentially** — the subagent tool awaits one child's result and disposes it before the parent's next tool call starts the next child — so their `createdAt` values are strictly ordered and match first-call order exactly. A same-millisecond sibling tie is therefore unreachable; the `recordedId` tiebreak only keeps such a degenerate collision deterministic, it does not recover first-call order. A future cut that runs siblings concurrently/backgrounded WOULD be able to create two children in the same millisecond, and must then thread a real first-call ordinal (the order live sessions first stream) rather than leaning on `createdAt` — flagged with `XXX(concurrent-subagents)` at the sort site.
 
+## Alternatives considered
+
 The alternative considered and rejected was a **call-ordered merge of the parent and child logs** into one global script (sound only because in-process subagent execution is strictly nested — the parent blocks on the child). It is simpler for today's synchronous cut but bakes in the parent-blocks-on-child invariant that a future backgrounded/concurrent subagent would break; per-session keying does not.
 
 ### 3. The harness harvests every log, primary-first