feat(models): OpenRouter model registry + interface + cron wiring (model-picker commit 1) (#13)

Foundation for the smart model picker. Fetches, normalizes, and caches
the OpenRouter model list (/api/v1/models — free, unauthenticated).
Daily refresh via the existing prautoblogger_daily_generation cron with
12h idempotency. 3-retry exponential backoff on transient failures;
serves last-good option payload when stale-and-fetch-fails.

New files:
- interface-model-registry.php — Phase 3-aware contract (94 lines)
- class-openrouter-model-registry.php — fetch + cache + query (226 lines)
- class-openrouter-model-normalizer.php — raw → standardized (114 lines)

Zero-coupling: no PRAUTOBLOGGER_* constants inside the service classes.
Config injected via constructor. Phase 2 lift into a shared Composer
package requires only namespace rename, zero internal edits.

Cost impact: $0/month (free endpoint, no LLM tokens).

Agent-Session: cowork-2026-04-16-model-picker-commit1

Co-authored-by: peptiderepo <peptiderepo@users.noreply.github.com>

CHANGELOG.md

@@ -8,6 +8,18 @@ and this project uses [Semantic Versioning](https://semver.org/).
 ## [Unreleased]
 
 ### Added
+- **OpenRouter model registry (model-picker commit 1).** Foundation for the
+  smart model picker: fetches, normalizes, and caches the OpenRouter model
+  list (`/api/v1/models` — free, unauthenticated). Daily refresh via the
+  existing `prautoblogger_daily_generation` cron hook with 12h idempotency.
+  - `includes/services/interface-model-registry.php` — Phase 3-aware contract.
+  - `includes/services/class-openrouter-model-registry.php` — fetch + cache + query.
+  - `includes/services/class-openrouter-model-normalizer.php` — raw → standardized shape.
+  - Capability vocabulary: `text→text`, `text+image→text`, `text→embedding`, etc.
+  - Zero-coupling: no PRAUTOBLOGGER_* constants inside the class — Phase 2 lift
+    into a shared Composer package requires only a namespace rename.
+  - Cost impact: $0/month (free endpoint, no LLM tokens).
+
 - **Image provider: Cloudflare Workers AI (FLUX.1 family).** First commit of
   the image + Instagram A/B pipeline workstream. Ships the provider, its
   pricing + validator helpers, four new settings fields in a new "Images"