fix: rename model registry files to match autoloader convention

The custom autoloader converts PRAutoBlogger_OpenRouter_Model_Registry
to class-open-router-model-registry.php (hyphen between Open and Router),
but the files were named class-openrouter-model-registry.php. This caused
a fatal "Class not found" error on every uncached page load.

Renames:
- class-openrouter-model-registry.php → class-open-router-model-registry.php
- class-openrouter-model-normalizer.php → class-open-router-model-normalizer.php

Updates @see references in interface, ARCHITECTURE.md, and CHANGELOG.md.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -40,8 +40,8 @@ and this project uses [Semantic Versioning](https://semver.org/).
   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.
+  - `includes/services/class-open-router-model-registry.php` — fetch + cache + query.
+  - `includes/services/class-open-router-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.