fix(signals): add a CRDT collaborative lore draft behind phase-141

[Olumide-01]

Closes #207

What this does

Concurrent edits to one signal clobber each other today. The existing
version + compare-and-swap contract is correct — it never lets a writer
silently overwrite a peer's row — but when many people type into the same
signal at once it answers the wrong question: one save wins and the rest
come back 409.

lib/__tests__/signal-crdt-benchmark.test.ts runs the workload the issue
specifies (50 writers, each editing from the same starting state without
seeing the others) against both strategies:

Strategy	Preserved	Outcome
version + CAS (current)	1/50	1 committed, 49 rejected with 409, text clobbered
Yjs CRDT draft (this PR)	50/50	50 updates folded into one snapshot, 0 rejected

So this layers a CRDT draft under the existing guard instead of
replacing it. The two solve different problems:

• A CRDT merges concurrent proposals. It cannot decide which text is
  authoritative, and it cannot write revertible history.
• The version guard decides what is authoritative, once, and records the
  pre-edit text so the revision stays revertible.

The commit path is still guarded

signal_crdt_docs / signal_crdt_updates are scratch state and never
write the signals row. A merged draft is promoted to committed lore only
through PUT /api/signals/[id] with from_draft: true, which lands in the
same editSignal CAS path as a manual edit and snapshots into
signal_versions as before.

Conflicts are still possible and still visible at that boundary: if a
colleague committed while your draft was open, PUT still answers 409
with current_version and a fresh ETag so the client can rebase. The
CRDT removes lost updates; it does not remove the need for a guard.

Changes

Area	File	Notes
Document model	lib/signal-crdt.ts	lore Y.Map of title/body Y.Text. Edits apply as a minimal prefix/suffix span diff, so two appends become two independent inserts instead of one overwriting the other.
Persistence	lib/signal-crdt-store.ts	Merges inside BEGIN IMMEDIATE; the update tail folds into the snapshot every 64 merges so it cannot grow unbounded. 256KB update cap.
Schema	lib/sqlite-db.ts	Two new tables plus an index. Purely additive, no migration.
API	app/api/signals/[id]/route.ts	Adds PUT (mandatory If-Match, requires both title and body so a revision is never half-applied). PATCH conflicts now carry current_version + ETag like the upvote path.
API	app/api/signals/[id]/crdt/route.ts	GET with ?state_vector= returns only the operations that client lacks; POST merges an update.
Client	app/signals/[id]/use-signal-crdt.ts	The hook await import()s the CRDT module, so Yjs stays out of the initial bundle while the flag is off.
UI	app/signals/[id]/signal-detail-client.tsx	Collaborative draft panel with sync state, contributor avatars, and a commit button.
Metrics	lib/signal-version-metrics.ts	signal_version_conflicts split by edit/put/upvote/reply, flagged separately when a CAS retry was attempted, plus CRDT merge and commit counters.
Store	lib/signal-store.ts	Emits the conflict metric at each existing guard.

Design decisions worth reviewing

HTTP, not WebSocket. The issue suggests prototyping Yjs over a
WebSocket. Yjs is transport-agnostic and its state-vector sync is a plain
request/response, so GET-with-state-vector carries the same wire format a
socket would without holding a connection open — and this app deploys to
Vercel serverless, where a long-lived socket per reader is not available.
The client posts on a short debounce and polls while the panel is open.

The store is the only thing that counts conflicts. An earlier draft
also incremented the metric in the route handler, which counted every
rejected CAS twice. Counters are aggregate only — no signal id, wallet, or
text ever reaches a label.

Flags. phase-141, defaulting off. Unset NEXT_PUBLIC_FEATURE_PHASE_141
and the CRDT routes return 404, the draft panel is hidden, and PUT still
works on its own as an If-Match-guarded full replacement. The
signal_crdt_* rows stay on disk as inert scratch state.

Testing

• 22 new tests in lib/__tests__/signal-crdt.test.ts, including 50
  concurrent writers with zero lost writes, reversed arrival order,
  idempotent re-submission, state-vector catch-up for a late replica, and
  two independent SQLite connections racing on the same file.
• Verified stable across 3 consecutive runs.
• npx tsc --noEmit: no new diagnostics. This also fixes a pre-existing
  break — diffLoreVersions was imported by the narrative versions route
  but never actually exported, because the file carried @ts-nocheck.
• Full suite: 319 passing. The 4 failures (nft-index-subscribe [SECURITY — WEBHOOK LEAK] Creator (100k NFTs) to evil.com and Exfiltrates All transfer Events Forever #228,
  world-roles-rbac [SECURITY — RBAC] world/[collection_id]/roles POST { wallet, role: 'admin' } Sans require_auth #291) were confirmed pre-existing on a stashed tree
  and are untouched by this PR.

Note on the issue title

This issue's title is about Soroban fee-bump and surge pricing, while the
body, evidence, and task list are about concurrent signal lore editing.
This PR addresses the body. Flagging in case the two should be split.

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