feat(models): OpenRouter model registry + interface + cron wiring (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 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

includes/services/interface-model-registry.php

@@ -0,0 +1,94 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Contract for a provider-specific AI model registry.
+ *
+ * Phase 1 (v1): single implementation for OpenRouter (`class-openrouter-model-registry.php`).
+ * Phase 3: a second implementation wraps Cloudflare Workers AI FLUX model data. A
+ * higher-level dispatcher iterates registered registries, calls each with the same
+ * capability, and unions the results — the per-registry interface stays unchanged.
+ *
+ * Implementations MUST:
+ *   - Store the normalized registry as a WP option + transient cache layer.
+ *   - Degrade gracefully when the source API is unreachable (serve last-good cache).
+ *   - Never throw on public read methods — empty arrays are acceptable fallbacks.
+ *   - Log refresh failures via PRAutoBlogger_Logger.
+ *
+ * Triggered by: Settings page field renderer (commit 2), AJAX refresh endpoint
+ *               (commit 3), daily cron via the main plugin loader.
+ * Dependencies: None at interface level — implementations wrap an HTTP API.
+ *
+ * @see services/class-openrouter-model-registry.php — Default implementation.
+ * @see admin/fields/class-openrouter-model-field.php — Field renderer that queries this interface.
+ * @see ARCHITECTURE.md                               — AI Model Registries section.
+ */
+interface PRAutoBlogger_Model_Registry_Interface {
+
+	/**
+	 * Return all models in the registry, normalized.
+	 *
+	 * @return array<int, array{
+	 *     id: string,
+	 *     name: string,
+	 *     provider: string,
+	 *     context_length: int,
+	 *     input_price_per_m: float,
+	 *     output_price_per_m: float,
+	 *     capabilities: string[],
+	 *     deprecated: bool,
+	 *     updated_at: int,
+	 * }> Normalized model records, sorted by name ascending.
+	 */
+	public function get_models(): array;
+
+	/**
+	 * Return only models matching a given capability string.
+	 *
+	 * @param string $capability One of the standardized capability strings:
+	 *                           'text→text', 'text+image→text', 'text+audio→text',
+	 *                           'text→image', 'text→audio', 'text→video',
+	 *                           'text→embedding'.
+	 *
+	 * @return array<int, array> Same record shape as get_models(), filtered.
+	 */
+	public function get_models_with_capability( string $capability ): array;
+
+	/**
+	 * Look up one model by its provider-qualified id (e.g. 'anthropic/claude-3.5-haiku').
+	 *
+	 * @param string $id Model identifier.
+	 *
+	 * @return ?array Normalized model record, or null if not in the registry.
+	 */
+	public function find_model( string $id ): ?array;
+
+	/**
+	 * Fetch fresh data from the upstream source and replace the cached payload.
+	 *
+	 * When `$force` is false, implementations SHOULD skip the HTTP call if the
+	 * payload is younger than a configured idempotency window (default 12h).
+	 *
+	 * Side effects: HTTP GET to the upstream API, wp_options write, transient set,
+	 *               log line on failure, admin notice flag on stale-and-failed.
+	 *
+	 * @param bool $force True to bypass the idempotency window (e.g. manual admin refresh).
+	 *
+	 * @return array{count: int, fetched_at: int} Number of models stored and unix timestamp.
+	 */
+	public function refresh( bool $force = false ): array;
+
+	/**
+	 * Unix timestamp of the last successful refresh. Zero if never refreshed.
+	 *
+	 * @return int
+	 */
+	public function get_fetched_at(): int;
+
+	/**
+	 * Machine-readable provider identifier (e.g. 'openrouter', 'cloudflare_workers_ai').
+	 *
+	 * @return string
+	 */
+	public function get_provider_name(): string;
+}