feat(lane0): fold review round 2 — FTS column, drop stale migrations

Closes the last Lane-0 schema items before the frozen base:

- events.search_tsv TSVECTOR GENERATED ALWAYS AS to_tsvector('simple',
  content) STORED + GIN idx_events_search_tsv. The Typesense->Postgres FTS
  data shape, landed in Lane 0 because it touches the just-locked events
  table (Quinn option A). GENERATED ALWAYS = single source of truth: proven
  against PG that a client cannot forge search_tsv out of sync with content
  (generated_always rejection). Index left minimal single-column GIN; the
  search lane picks the final spelling after EXPLAIN (Max's caveat).
- Delete stale 0002_backfill_d_tag.sql / 0003_event_reminders.sql. In the
  consolidated-from-scratch model 0001 already carries d_tag, not_before,
  delivered_at, and idx_events_not_before; re-running the old additive
  migrations would error (duplicate column / duplicate index name).

audit_log DDL shape confirmed for the audit-crate collapse (Dawn's lane):
PRIMARY KEY (community_id, seq), UNIQUE (community_id, hash), community_id
NOT NULL on every row. 0001 is the single source; buzz-audit drops its own
schema.rs / AUDIT_SCHEMA_SQL / ensure_schema() in the audit lane.

Re-proven against real Postgres — full fence suite green: T1 re-tenant
rejected, T6 cross-community member FK rejected, T6b same-community ok, T7
same channel UUID in two communities allowed, T8 host case-collision
rejected, T9 same event id in two communities allowed, plus the FTS
generated+GIN match and the forge-rejection. buzz-core: 189 + 2 doctests.

Co-authored-by: Tyler Longwell <tlongwell@block.xyz>
Signed-off-by: Tyler Longwell <tlongwell@block.xyz>

migrations/0001_initial_schema.sql

@@ -195,6 +195,15 @@ CREATE TABLE events (
     kind        INT NOT NULL,
     tags        JSONB NOT NULL,
     content     TEXT NOT NULL,
+    -- Full-text search vector (Typesense → Postgres FTS). Generated/STORED so
+    -- it is a single source of truth — no sidecar indexer to keep coherent
+    -- (Quinn option A, Lane-0 call). 'simple' config = no stemming/stopwords,
+    -- matching the existing substring-ish search semantics; the search lane can
+    -- revisit the config behind evidence. Tenant scoping is by the
+    -- community-leading btree filters BitmapAnd-ed with the GIN probe, so the
+    -- GIN index itself stays the minimal `GIN (search_tsv)` (Max's caveat:
+    -- avoid btree_gin unless EXPLAIN proves it buys something).
+    search_tsv  TSVECTOR GENERATED ALWAYS AS (to_tsvector('simple', content)) STORED,
     sig         BYTEA NOT NULL,
     received_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
     channel_id  UUID,
@@ -242,6 +251,11 @@ CREATE INDEX idx_events_parameterized
     WHERE d_tag IS NOT NULL AND deleted_at IS NULL;
 CREATE INDEX idx_events_not_before ON events (community_id, not_before)
     WHERE not_before IS NOT NULL AND deleted_at IS NULL AND delivered_at IS NULL;
+-- Full-text search. Minimal GIN over the generated tsvector; community scoping
+-- is supplied by the community-leading btree filters above (BitmapAnd), so this
+-- stays a single-column GIN. The search lane confirms the final spelling with
+-- EXPLAIN before its work lands (Quinn option A; Max's index-spelling caveat).
+CREATE INDEX idx_events_search_tsv ON events USING GIN (search_tsv);
 
 -- ── Event mentions ────────────────────────────────────────────────────────────
 -- Conformance: "Channel-less global events and DMs" (#p fan-out). The join to

migrations/0002_backfill_d_tag.sql

@@ -1,17 +0,0 @@
--- Backfill d_tag for existing NIP-33 range events (kind 30000–39999).
--- Idempotent: only updates rows where d_tag is still NULL.
--- Includes soft-deleted rows so the column is fully populated.
--- Run once after adding the d_tag column to the events table.
---
--- Managed by sqlx migrations.
-
-UPDATE events
-SET d_tag = COALESCE(
-    (SELECT elem->>1
-     FROM jsonb_array_elements(tags) AS elem
-     WHERE elem->>0 = 'd'
-     LIMIT 1),
-    ''
-)
-WHERE kind BETWEEN 30000 AND 39999
-  AND d_tag IS NULL;

migrations/0003_event_reminders.sql

@@ -1,17 +0,0 @@
--- Add NIP-ER event-reminder columns and due-delivery index to the events table.
---
--- `not_before` is the reminder's scheduled delivery time (Unix seconds);
--- `delivered_at` records when the scheduler published it. Both are nullable —
--- non-reminder events leave them NULL. The partial index covers only
--- undelivered, live reminders so the scheduler's due-query stays cheap.
---
--- `events` is partitioned by RANGE (created_at); ALTER TABLE on the parent
--- cascades the columns to every partition, and CREATE INDEX on the parent
--- builds a partitioned index that propagates to each partition.
---
--- Managed by sqlx migrations.
-
-ALTER TABLE events ADD COLUMN not_before BIGINT;
-ALTER TABLE events ADD COLUMN delivered_at BIGINT;
-CREATE INDEX idx_events_not_before ON events (not_before)
-    WHERE not_before IS NOT NULL AND deleted_at IS NULL AND delivered_at IS NULL;