feat(tools): DB-backed LLM engine admin (owner-only)

Add an owner-gated dashboard to remap any tool/tier's model live without a
code push. Overrides live in dbn_tool_engine_config (dobetternorge_maindb)
and are consulted by dbnToolsResolveToolRun() + dbnToolsReviewerModel();
no row = unchanged code/.env behaviour (fully back-compatible).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

includes/ToolModels.php

@@ -91,6 +91,22 @@ final class ToolModels
         return self::QUALITY_TIERS[self::qualityTier($tier)]['engine'];
     }
 
+    /**
+     * Engine keys the gateway layer can route for the tier/legacy tools. This is the
+     * allowlist an operator override (dbn_tool_engine_config) is validated against, so a
+     * bad DB value can never produce an unroutable engine string.
+     */
+    public static function tierEngineKeys(): array
+    {
+        return ['nova_lite', 'azure_mini', 'azure_full', 'gpu', 'regex', 'claude_haiku', 'claude_sonnet'];
+    }
+
+    /** True if $engine is a routable tier/legacy engine key. */
+    public static function isValidTierEngine(string $engine): bool
+    {
+        return in_array($engine, self::tierEngineKeys(), true);
+    }
+
     /** Human label for a quality tier (UI / telemetry). */
     public static function tierLabel(string $tier): string
     {