feat: import Chinese-localized Buzz source snapshot

Signed-off-by: cls_宁波本机 <908705107@qq.com>

scripts/cutover/README.md

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+# 1321 cutover: single-community → multi-tenant
+
+`1321_backfill_default_community.sql` is a **one-off operator script**, not a
+startup migration. It takes a pre-1321 (single-community) Buzz Postgres to the
+1321 multi-tenant schema, assigning every existing row to one default community
+derived from the deployment host.
+
+> It is **not** embedded in the relay binary. The relay's `sqlx::migrate!`
+> embeds only `migrations/0001_initial_schema.sql` — the consolidated 1321
+> schema. Fresh deployments need only that; this script exists solely to carry
+> existing pre-1321 data across the rewrite. (It uses psql client features —
+> `\set`, `\ir`, `:'var'` interpolation, `\gset` — that the embedded sqlx
+> migrator cannot run, which is why it must live here and not under
+> `migrations/`.)
+
+## When you need it
+
+Only when upgrading a Postgres that already holds **pre-1321 single-community
+data** to 1321. A brand-new deployment does **not** run this — it provisions
+from `migrations/0001_initial_schema.sql` (or `schema/schema.sql`) directly.
+
+## Preconditions
+
+- The DB is pristine pre-1321: no `communities` table, no `community_id`
+  columns, no leftover `legacy` schema. The script's guard **refuses to run**
+  otherwise (already-migrated, partially-migrated, or failed-prior-run states
+  all raise and abort — see the guard block at the top of the script).
+- **Take a `pg_dump` / PVC snapshot first.** There is no down-path. The
+  snapshot **is** the rollback.
+
+## Run it
+
+The whole script runs in **one transaction** (all-or-nothing). Pass the
+deployment host as `:host`; it is normalized exactly as the relay normalizes a
+community host (`rtrim(lower(host), '.')`).
+
+```sh
+psql "$DATABASE_URL" \
+     -v host="'your-deployment-host.example.com'" \
+     -v ON_ERROR_STOP=1 \
+     -f scripts/cutover/1321_backfill_default_community.sql
+```
+
+`-f` (not stdin) matters: the script `\ir`-includes
+`../../migrations/0001_initial_schema.sql` **relative to its own location**, so
+it resolves the canonical 1321 schema regardless of your cwd.
+
+### What it does
+
+1. Renames all pre-1321 tables and enum types aside into a `legacy` schema.
+2. `\ir`-includes the repo's `0001` verbatim → the correct 1321 schema in a
+   clean `public` (structurally identical to a fresh 1321 DB **by
+   construction** — no hand-transcription).
+3. Creates the one default community from `:host`.
+4. Copies every row forward, stamped with that `community_id` (`search_tsv`
+   regenerates as GENERATED; new-in-1321 columns default NULL).
+5. `DROP SCHEMA legacy CASCADE`.
+
+## After it commits
+
+Boot the 1321 relay with **`BUZZ_AUTO_MIGRATE=false`**. The schema is already
+correct; the relay's idempotent boot-time `ensure_configured_community` /
+allowlist→relay_members backfill finds this community and no-ops.
+
+If you want the relay's sqlx migrator to consider `0001` already applied (so a
+later `BUZZ_AUTO_MIGRATE=true` boot doesn't try to re-run it), seed its
+`_sqlx_migrations` row to match a fresh 1321 install:
+
+```sql
+-- version 1, description 'initial schema'; checksum must match the embedded 0001.
+-- Easiest: diff _sqlx_migrations against a freshly-migrated 1321 DB and copy the row.
+```
+
+This is **not** required for correct operation — a fresh `0001` run against the
+already-correct schema is a no-op only if the migrator's checksum matches, so
+prefer leaving `BUZZ_AUTO_MIGRATE=false` unless you have a reason to seed.
+
+## Verify (post-commit, outside the txn)
+
+```sql
+SELECT count(*) FROM communities;                       -- expect 1
+SELECT count(*) FROM events WHERE community_id IS NULL;  -- expect 0
+SELECT to_regnamespace('legacy');                        -- expect NULL (gone)
+```
+
+For a stronger guarantee, take a constraint/trigger/index/column diff of this
+DB against a freshly-migrated 1321 DB — it should be empty.