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>

includes/class-autoloader.php

@@ -26,6 +26,7 @@ class PRAutoBlogger_Autoloader {
 		'providers/',
 		'models/',
 		'frontend/',
+		'services/',
 	];
 
 	/**