BUZZ-301: Add user deletion request intake (#8496)

## Summary

Add the first testable piece of user deletion: submit a synthetic
request, list requests, and inspect one by UUID. Operators can verify
that intake reaches PostgreSQL before we add inventory, approval, and
execution.

Add one operator-global `entity_deletion_requests` table with an
additive migration and matching desired-state schema. Identical
submissions return the same row. Conflicting submissions fail without
changing it. Only `demo:` targets are accepted, and requests stay
`submitted`.

Keep the commands in `buzz-deletion`, reached through a thin `buzz-admin
user-deletions` adapter. Reuse the existing database connection setup.
This change adds no worker, stage history, community gates, or deletion
operations.

### Rollout plan

This is an expand-only schema change plus an operator CLI. Existing
relay code does not use the new request table. No backfill or real
deletion is part of this release.

1. **Order the PRs.** Land #8496 first, using 0068; main now owns 0067
for channel join roles. Rework #8489 to build on this table with the
next available migration number. Renumbering its existing CREATE TABLE
migration alone is insufficient; both PRs currently create the same
request table.
2. **Apply on staging.** For deployments that manage schema separately,
apply the reviewed additive migration before using the new CLI. Where
auto-migration is enabled, the new relay binary applies it at startup.
Keep existing tables and records unchanged.
3. **Verify on staging.** Use the new `buzz-admin` binary with
`DATABASE_URL` pointing to staging. Submit a unique synthetic label,
list requests, and inspect the returned UUID:

   ```bash
buzz-admin user-deletions submit --target demo:staging-intake-1
--requested-by <operator>
   buzz-admin user-deletions list --limit 5
   buzz-admin user-deletions inspect <returned-uuid>
   ```

Verify one `entity_deletion_requests` row with status `submitted`.
Repeat the identical submission and verify the same UUID and timestamps.
Use a new label if this label was used by an earlier staging test.
4. **Apply beyond staging.** After verification, use the deployment's
reviewed schema/release workflow to add the table in the remaining
environments. Requests run only through the operator CLI; this release
starts no deletion worker. No feature flag is needed for this synthetic
intake: the database accepts only `demo:` targets, and real deletion is
absent.
5. **Rollback.** Keep the additive table and saved requests; stop using
the new commands and roll back the binary if needed. After 0068 is
applied, an older binary with auto-migration enabled can fail at startup
with sqlx `VersionMissing`. A binary rollback therefore requires
migration execution to be disabled on the older relay
(`BUZZ_AUTO_MIGRATE=false`, including the corresponding deployment
configuration).

### Related work

This is a smaller first slice of the full-workflow draft
[#8489](https://github.com/block/buzz/pull/8489), which is preserved for
later extraction. The two PRs overlap and should not both be merged as
written.

### Testing

The author submitted `demo:rarora-manual-1` to a separate local
PostgreSQL 17 database. Repeating the same submission returned its
original UUID and timestamps. List, inspect, and a direct SQL query all
returned the same saved request.

<details>
<summary>Actual command inputs and outputs</summary>

Commands ran from the new worktree with `DATABASE_URL` set to the local
`buzz_user_deletion_submit` database. Outputs below are stdout;
connection diagnostics on stderr are omitted.

**Submit again — returns the existing request without creating a
duplicate**

```bash
./target/debug/buzz-admin user-deletions submit \
  --target demo:rarora-manual-1 --requested-by rarora
```

```json
{
  "id": "2e5bcdec-ab68-44d2-9743-1dd9fa7d2f89",
  "entity_type": "user",
  "target": "demo:rarora-manual-1",
  "status": "submitted",
  "requested_by": "rarora",
  "reason": null,
  "created_at": "2026-10-20T19:57:44.516698Z",
  "updated_at": "2026-10-20T19:57:44.516698Z"
}
```

**List saved requests**

```bash
./target/debug/buzz-admin user-deletions list --limit 5
```

```json
[
  {
    "id": "2e5bcdec-ab68-44d2-9743-1dd9fa7d2f89",
    "entity_type": "user",
    "target": "demo:rarora-manual-1",
    "status": "submitted",
    "requested_by": "rarora",
    "reason": null,
    "created_at": "2026-10-20T19:57:44.516698Z",
    "updated_at": "2026-10-20T19:57:44.516698Z"
  }
]
```

**Inspect one request**

```bash
./target/debug/buzz-admin user-deletions inspect 2e5bcdec-ab68-44d2-9743-1dd9fa7d2f89
```

```json
{
  "id": "2e5bcdec-ab68-44d2-9743-1dd9fa7d2f89",
  "entity_type": "user",
  "target": "demo:rarora-manual-1",
  "status": "submitted",
  "requested_by": "rarora",
  "reason": null,
  "created_at": "2026-10-20T19:57:44.516698Z",
  "updated_at": "2026-10-20T19:57:44.516698Z"
}
```

**Read the table directly**

```bash
docker exec buzz-user-deletion-dev-20261020 \
  psql -X -U buzz -d buzz_user_deletion_submit -c \
  "SELECT id, entity_type, target, status, requested_by
   FROM entity_deletion_requests ORDER BY created_at DESC;"
```

```text
                  id                  | entity_type |        target        |  status   | requested_by 
--------------------------------------+-------------+----------------------+-----------+--------------
 2e5bcdec-ab68-44d2-9743-1dd9fa7d2f89 | user        | demo:rarora-manual-1 | submitted | rarora
(1 row)
```

</details>

A separate CLI smoke test also verified that a conflicting operator and
a non-demo target fail without changing the saved request. The existing
community-deletion `list --limit 1` command passed against the smoke
database.

See [the intake
walkthrough](729233c726/docs/operator-user-deletion-intake.md)
for setup, commands, expected fields, and the SQL query.

Generated with Codex

---------

Signed-off-by: Ravneet Arora <rarora@squareup.com>

schema/schema.sql

@@ -122,6 +122,7 @@ CREATE EXTENSION IF NOT EXISTS pgcrypto;
 \i tables/public/push_gateway_delivery_request_replays.sql
 \i tables/public/replica_heartbeat.sql
 \i tables/public/community_deletion_requests.sql
+\i tables/public/entity_deletion_requests.sql
 \i tables/public/community_deletion_approvals.sql
 \i tables/public/community_deletion_checkpoints.sql
 \i tables/public/community_deletion_manifest_keys.sql
@@ -194,6 +195,7 @@ CREATE EXTENSION IF NOT EXISTS pgcrypto;
 \i seeds/push_gateway_delivery_request_replays.sql
 \i seeds/replica_heartbeat.sql
 \i seeds/community_deletion_requests.sql
+\i seeds/entity_deletion_requests.sql
 \i seeds/community_deletion_approvals.sql
 \i seeds/community_deletion_checkpoints.sql
 \i seeds/community_deletion_manifest_keys.sql