fix(schema): normalize federation_peers.consecutive_failures to NOT NULL

The column was `integer DEFAULT 0` (nullable) since the initial schema.
Counters should not be nullable — the semantics are a count, not an
optional measurement. `consecutive_auth_failures` (added later) was
correctly declared NOT NULL; tightening `consecutive_failures` to match
removes the drift and eliminates the "|null" burden everywhere the value
is read.

SQLite does not support in-place ALTER … SET NOT NULL, so drizzle-kit
cannot auto-generate this. The manual migration uses the standard
SQLite recreate pattern (new table + INSERT SELECT + DROP + RENAME +
recreate index) under `PRAGMA defer_foreign_keys = ON` so the existing
federation_outbox → federation_peers FK survives the swap. The COPY
step coalesces any hypothetical NULL to 0 defensively; live probes on
both test instances (nova, orbit) showed zero NULL rows so no
actual backfill is required.

Verified by applying the full migration chain against a copy of the VM's
live DB: column ends as `notnull=1 dflt=0`, the peer row is preserved,
the unique index on origin is recreated, NULL inserts are rejected, and
`PRAGMA foreign_key_check` reports no violations.

Server `SanitizedPeer.consecutiveFailures` tightened to `number` to
match the new drizzle inference and the shared `FederationPeer` shape.

Follow-up #22 from S2S DM unification backlog.

packages/server/drizzle/meta/_journal.json

@@ -29,6 +29,13 @@
       "when": 1776789567488,
       "tag": "0003_classy_loki",
       "breakpoints": true
+    },
+    {
+      "idx": 4,
+      "version": "6",
+      "when": 1776802580650,
+      "tag": "0004_cooing_black_knight",
+      "breakpoints": true
     }
   ]
 }