Phase 10: hardening and ops

Implements PLAN.md Phase 10.

Simplified Sliding Sync (MSC4186) is served at the unstable
org.matrix.simplified_msc3575 endpoint and advertised in /versions. Lists
are sorted by activity and filtered by DM, invite, encryption, room type,
space and tag; room subscriptions, required_state with wildcards, $ME and
$LAZY, and the to_device, e2ee, account_data, receipts and typing
extensions are supported. Per-connection state is kept in memory and an
unknown pos answers M_UNKNOWN_POS.

Threads and relations: m.relates_to is indexed on roomserver_events
(migration 0012), /relations (with recursion) and /threads are served, and
every event a timeline read returns carries its m.thread, m.replace and
m.reference summaries in unsigned.m.relations. Notifications carry a
thread ID (migration 0013): threaded receipts clear only their thread, and
sync reports unread_thread_notifications when the filter asks.

Spaces: /hierarchy walks a space breadth first, asking other servers about
rooms this one is not in through the new federation hierarchy endpoint;
room_summary describes one room. /search runs on FTS5 (sqlite, pocketbase)
or tsvector (postgres), bounded to what each user may see, with context,
profiles, state, grouping and paging.

The PocketBase driver is real: the sqlite schema and store on an embedded
PocketBase app's database, with media in its filesystem, local or S3
(database.pocketbase.s3). It runs the full storage test suite.

Ops: OpenTelemetry tracing over OTLP/HTTP (tracing.*), with server spans
per route, component spans, and trace propagation on federation, push and
application service calls. New metrics for persisted events, waiting
syncs, sliding sync connections and the database pool, with a Grafana
dashboard. deploy/ adds a Compose setup (PostgreSQL, Prometheus, Grafana,
Jaeger) and a Helm chart; cmd/warp-loadtest loads a server and reports
request and delivery latencies.

The load tester found a long-standing bug, fixed here: on a server where
no account data had been written, every incremental /sync re-sent the push
rules and returned at once, and an all-zero token was taken for an initial
sync, so long polls became busy loops.

The PostgreSQL migrations and search dialect compile but were not run
against a live PostgreSQL in this change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/development.md

@@ -47,7 +47,8 @@ WARP_SERVER_NAME=dev.local WARP_PRIVATE_KEY=./keys/dev.key ./bin/warp serve
 1. Write the same change twice, once per SQL dialect:
    `server/internal/storage/sqlite/migrations/NNNN_name.sql` and
    `server/internal/storage/postgres/migrations/NNNN_name.sql`.
-   Use the next free number; `NNNN` is zero-padded to four digits.
+   Use the next free number; `NNNN` is zero-padded to four digits. The
+   pocketbase driver uses the SQLite files as they are.
 2. The files are embedded with `embed.FS`, so a rebuild picks them up.
 3. `./bin/warp migrate --status` lists what would run, `./bin/warp migrate`
    applies it. A server started with `database.auto_migrate: true` (the
@@ -124,7 +125,9 @@ says why.
   smaller set that goes through the whole wrapped handler, to catch a route
   that was written but never registered.
 - Storage tests run against every driver that is available:
-  SQLite always, PostgreSQL when `WARP_TEST_POSTGRES_DSN` is set. The
+  SQLite and PocketBase always, PostgreSQL when `WARP_TEST_POSTGRES_DSN` is
+  set. PocketBase runs the SQLite migrations on PocketBase's own database,
+  so a SQLite migration is a PocketBase one too. The
   PostgreSQL tests share one database, so each group of them truncates the
   tables it owns first; add a table to `resetRoomTables` or
   `resetSyncTables` when you add one, or the second test to insert the same