feat(05-04): extend Tier 1 provider verify specs

- 12 Tier 1 providers now carry success_codes, failure_codes, rate_limit_codes
- {{KEY}} template in headers or URL (double-brace canonical form)
- metadata_paths added where provider APIs return useful metadata
- Anthropic switched to POST /v1/messages with minimal body
- Perplexity gains JSON body, content-type header
- Inflection verify URL left empty (no public endpoint)
- Dual-location sync preserved: providers/ mirrors pkg/providers/definitions/

providers/xai.yaml

@@ -15,6 +15,10 @@ verify:
   method: GET
   url: https://api.x.ai/v1/api-key
   headers:
-    Authorization: "Bearer {KEY}"
-  valid_status: [200]
-  invalid_status: [401, 403]
+    Authorization: "Bearer {{KEY}}"
+  success_codes: [200]
+  failure_codes: [401, 403]
+  rate_limit_codes: [429]
+  metadata_paths:
+    name: "name"
+    acls: "acls"