feat(agent): switch LLM client from Ollama to OpenAI-compatible API (LM Studio support)

- Replace /api/chat with /v1/chat/completions endpoint
- Use json_schema response_format (LM Studio does not support json_object)
- Make schema parameter optional in call_ollama to support different schemas per use case
- Add dedicated normalize schema (normalized_metadata) with release_kind field
  instead of release_type to avoid model repetition loops
- Add dedicated merge schema (artist_merge) so model no longer confuses
  normalize and merge response structures
- Add retry with frequency_penalty=1.5 on parse failure to suppress repetition
- Add id3 crate as fallback metadata reader for MP3 files with large embedded
  cover art that exceed Symphonia probe limit of 1MB

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

furumi-agent/src/merge.rs

@@ -35,12 +35,38 @@ pub async fn propose_merge(state: &Arc<AppState>, merge_id: Uuid) -> anyhow::Res
 
     let user_message = build_merge_message(&artists_data);
 
+    let schema = serde_json::json!({
+        "type": "object",
+        "properties": {
+            "canonical_artist_name": { "type": "string" },
+            "winner_artist_id":      { "type": "integer" },
+            "album_mappings": {
+                "type": "array",
+                "items": {
+                    "type": "object",
+                    "properties": {
+                        "source_album_id":     { "type": "integer" },
+                        "canonical_name":      { "type": "string" },
+                        "merge_into_album_id": { "type": ["integer", "null"] }
+                    },
+                    "required": ["source_album_id", "canonical_name", "merge_into_album_id"],
+                    "additionalProperties": false
+                }
+            },
+            "notes": { "type": "string" }
+        },
+        "required": ["canonical_artist_name", "winner_artist_id", "album_mappings", "notes"],
+        "additionalProperties": false
+    });
+
     let response = call_ollama(
         &state.config.ollama_url,
         &state.config.ollama_model,
         &state.merge_prompt,
         &user_message,
         state.config.ollama_auth.as_deref(),
+        0.5,
+        Some(("artist_merge", schema)),
     ).await?;
 
     let proposal = parse_merge_response(&response)?;