feat(devices): pairing codes replace the registration broadcast

A pending device registration used to be announced to EVERY account's
Devices page, and whoever clicked Approve first bound the device — and
its freshly minted sync token — to their account. Worse, the pending
card displayed the registration UUID, which is also the bearer
credential on the unauthenticated /api/devices/register/status poll
channel: any family user who could see the list already held everything
needed to take the device. On a family server that is a
wrong-account-binding bug (accidental or deliberate); this commit
removes the class of problem rather than patching the race.

The new model is the Netflix/YouTube TV device flow: the registering
device displays a 6-digit pairing code, and the only person who can
read it — whoever holds the device — types it into THEIR account on the
Devices page. Possession of the device screen becomes the credential;
nothing is broadcast; the reject-on-someone-else's-behalf hole dies
with the list.

Server changes:
- POST /api/devices/register now mints pairing_code (crypto/rand,
  rejection-sampled for uniformity, collision-checked against live
  registrations) and retires prior unclaimed registrations with the
  same device_identifier, so re-registering leaves exactly one live
  attempt.
- POST /api/devices/claim (JWT) binds the registration behind a code to
  the caller's account, reusing the rotate-or-create approval logic
  factored out of ApproveDevice (shared bindRegistrationToUser helper;
  the Android self-approval route keeps working unchanged).
- POST /api/devices/claim/lookup (JWT) returns the confirm-card data
  without binding. Lookup and claim share a per-account budget (12
  attempts/min, DeviceRateLimiter gained a claim case) — the 1M-code
  space over a 5-minute TTL makes guessing infeasible without it.
- POST /api/devices/register/cancel lets the registering device end its
  own attempt (registration UUID bearer, idempotent, never touches a
  claimed registration).
- ListPendingRegistrations / GetPendingRegistrationsData are
  deprecated-by-emptiness: unclaimed registrations return to nobody.
- RejectDevice and its route are deleted — the broadcast list was its
  only consumer, and there is nothing left for anyone to reject.

Additive-only for pinned surfaces: the register response gains
pairing_code (Android DTO untouched), the four KOReader sync surfaces
and approve keep byte-identical shapes. contract_pins.md changelog
records the widening and the reject removal. Docs, schema registry, and
bruno mirrors move together per the drift gate; bruno_gen.go now keeps
hand-authored bruno/podcasts/ (API docs never existed for them, so the
next -update run would have swept them — latent landmine, defused).

Unit tests: code shape, live-collision avoidance, typed-code
normalization, and the resolve scopes (live/expired/claimed/miss).

bruno/devices/claim_device.yml

@@ -0,0 +1,37 @@
+info:
+  name: Claim Device (Pairing Code)
+  type: http
+  seq: 4
+
+http:
+  method: POST
+  url: '{{base_url}}/api/devices/claim'
+  auth: inherit
+  body:
+    type: json
+    data: |-
+      {
+        "pairing_code": "583912"
+      }
+settings:
+  encodeUrl: true
+  timeout: 0
+  followRedirects: true
+  maxRedirects: 5
+
+runtime:
+  scripts:
+    - type: tests
+      code: |-
+        test("status is 200", function() {
+          expect(res.status).to.eql(200);
+        });
+
+docs:
+  content: |-
+    # Claim Device (Pairing Code)
+
+    `POST /api/devices/claim` — auth: jwt.
+
+    Canonical reference: docs/developer/api/devices/claim_device.md (docs site → Developer → API). This request is GENERATED from that doc; edit the doc, then run the drift test with -update.
+  type: text/markdown