feat(docs): add Bruno API collection for relay endpoints

Adds a Bruno HTTP client collection covering all four relay endpoints
(health, describeServer, claim-codes, create-signing-key) with a local
environment template and a mandatory update rule in CLAUDE.md.

CLAUDE.md

···
 - `nixosModules.default` - NixOS module exposing `services.ezpds` options (see `nix/CLAUDE.md`)
 - `devShells.<system>.default` - Development shell via devenv
 
+## Bruno API Collection
+- `bruno/` - Bruno HTTP client collection for all relay endpoints
+- Open in Bruno desktop app; select the `local` environment and set `adminToken` to your relay admin token
+- **Mandatory:** When adding, removing, or changing any route (path, method, request body, response shape, auth), update the corresponding `.bru` file in `bruno/`. New routes get a new `.bru` file with the next `seq` number.
+
 ## Conventions
 - Workspace-level dependency versions in root Cargo.toml; crates use `{ workspace = true }`
 - All crates share version (0.1.0) and edition (2021) via workspace.package

bruno/bruno.json

···
+{
+  "version": "1",
+  "name": "ezpds",
+  "type": "collection",
+  "ignore": [
+    "node_modules",
+    ".git"
+  ],
+  "size": 0.0007619857788085938,
+  "filesCount": 5,
+  "presets": {
+    "requestType": "http",
+    "requestUrl": "http://localhost:8080"
+  }
+}

bruno/claim_codes.bru

···
+meta {
+  name: Claim Codes
+  type: http
+  seq: 3
+}
+
+post {
+  url: {{baseUrl}}/v1/accounts/claim-codes
+  body: json
+  auth: bearer
+}
+
+auth:bearer {
+  token: {{adminToken}}
+}
+
+body:json {
+  {
+    "count": 1,
+    "expiresInHours": 24
+  }
+}

bruno/create_signing_key.bru

···
+meta {
+  name: Create Signing Key
+  type: http
+  seq: 4
+}
+
+post {
+  url: {{baseUrl}}/v1/relay/keys
+  body: json
+  auth: bearer
+}
+
+auth:bearer {
+  token: {{adminToken}}
+}
+
+body:json {
+  {
+    "algorithm": "p256"
+  }
+}

bruno/describe_server.bru

···
+meta {
+  name: Describe Server
+  type: http
+  seq: 2
+}
+
+get {
+  url: {{baseUrl}}/xrpc/com.atproto.server.describeServer
+  body: none
+  auth: none
+}
+
+vars:pre-request {
+  baseUrl: http://localhost:8080
+}

bruno/environments/local.bru

···
+vars {
+  baseUrl: http://localhost:8080
+  adminToken: your-admin-token-here
+}

bruno/health.bru

···
+meta {
+  name: Health Check
+  type: http
+  seq: 1
+}
+
+get {
+  url: {{baseUrl}}/xrpc/_health
+  body: none
+  auth: none
+}
+
+vars:pre-request {
+  baseUrl: http://localhost:8080
+}