feat: Structured prompt editing for Pro model

Backend:
- Added prompt_structure JSON column to clips DB (migration in init_db)
- Updated GenerateRequest model with optional prompt_structure dict
- build_prompt() method combines structured fields into single prompt:
  'Generate a track with the following elements:\n\n**Style:** [style]\n...'
- create_clip() accepts and stores prompt_structure JSON
- get_clips()/get_clip() parse prompt_structure back to dict

Frontend:
- New StructuredPromptEditor component with 8 collapsible fields:
  Style, Timbre, Structure, Mood, Tempo, Instrumentation, Effects, Additional
  - Fields show filled/empty state with colored dots
  - Expand/collapse individual fields
  - 'Expand All' button
  - Counter: 'X of 8 fields filled'
- Generator component updated with Basic/Advanced mode toggle (Pro only)
  - Basic: single textarea (works for both models)
  - Advanced: StructuredPromptEditor (Pro only)
  - Mode resets to Basic when switching to Clip Preview
- DetailPanel shows structured prompt breakdown when present
  - Each filled field shown in its own labeled box
  - Style, Timbre, Structure, Mood, Tempo, Instrumentation, Effects, Additional
- Clip interface updated with prompt_structure field across all components

Architecture KB and Tasks KB updated.

backend/src/database.py

@@ -78,15 +78,20 @@ async def init_db():
             await db.execute("ALTER TABLE clips ADD COLUMN key TEXT")
         except Exception:
             pass  # Column already exists
+        # Migration: add prompt_structure column if it doesn't exist
+        try:
+            await db.execute("ALTER TABLE clips ADD COLUMN prompt_structure TEXT")
+        except Exception:
+            pass  # Column already exists
         await db.commit()
 
-async def create_clip(prompt: str, model: str, duration: int) -> str:
+async def create_clip(prompt: str, model: str, duration: int, prompt_structure: str = None) -> str:
     clip_id = str(uuid.uuid4())
     filename = f"{clip_id}.mp3"
     async with aiosqlite.connect(DB_PATH) as db:
         await db.execute(
-            "INSERT INTO clips (id, prompt, model, duration_seconds, filename, status) VALUES (?, ?, ?, ?, ?, ?)",
-            (clip_id, prompt, model, duration, filename, "generating")
+            "INSERT INTO clips (id, prompt, model, duration_seconds, filename, status, prompt_structure) VALUES (?, ?, ?, ?, ?, ?, ?)",
+            (clip_id, prompt, model, duration, filename, "generating", prompt_structure)
         )
         await db.commit()
     return clip_id
@@ -121,6 +126,13 @@ async def get_clips(limit: int = 50, offset: int = 0):
             clips = [dict(row) for row in rows]
             for clip in clips:
                 clip["created_at"] = format_timestamp(clip.get("created_at"))
+                # Parse prompt_structure JSON
+                if clip.get("prompt_structure"):
+                    try:
+                        import json
+                        clip["prompt_structure"] = json.loads(clip["prompt_structure"])
+                    except Exception:
+                        clip["prompt_structure"] = None
             return clips
 
 async def get_clip(clip_id: str):
@@ -131,6 +143,13 @@ async def get_clip(clip_id: str):
             if row:
                 clip = dict(row)
                 clip["created_at"] = format_timestamp(clip.get("created_at"))
+                # Parse prompt_structure JSON
+                if clip.get("prompt_structure"):
+                    try:
+                        import json
+                        clip["prompt_structure"] = json.loads(clip["prompt_structure"])
+                    except Exception:
+                        clip["prompt_structure"] = None
                 return clip
             return None
 

backend/src/main.py

@@ -77,13 +77,18 @@ async def _generate_and_save(clip_id: str, prompt: str, model: str, duration: in
 @app.post("/api/generate", response_model=GenerateResponse)
 async def generate(request: GenerateRequest, background_tasks: BackgroundTasks):
     duration = request.get_effective_duration()
-    clip_id = await create_clip(request.prompt, request.model, duration)
+    # Build prompt from structured fields if present
+    final_prompt = request.build_prompt()
+    # Serialize structured prompt for DB storage
+    import json
+    prompt_structure_json = json.dumps(request.prompt_structure) if request.prompt_structure else None
+    clip_id = await create_clip(final_prompt, request.model, duration, prompt_structure_json)
     
     # Kick off generation in background
     background_tasks.add_task(
         _generate_and_save,
         clip_id,
-        request.prompt,
+        final_prompt,
         request.model,
         duration
     )

backend/src/models.py

@@ -24,6 +24,7 @@ class GenerateRequest(BaseModel):
     prompt: str
     model: str = DEFAULT_MODEL
     duration: Optional[int] = None  # defaults to model default
+    prompt_structure: Optional[dict] = None  # structured prompt fields for Pro mode
 
     @field_validator('model')
     @classmethod
@@ -40,6 +41,26 @@ class GenerateRequest(BaseModel):
         dur = self.duration if self.duration is not None else info["default_duration"]
         return min(dur, info["max_duration"])
 
+    def build_prompt(self) -> str:
+        """Build the final prompt from structured fields or return the simple prompt."""
+        if self.prompt_structure:
+            parts = ["Generate a track with the following elements:"]
+            field_order = [
+                ("style", "Style"),
+                ("timbre", "Timbre"),
+                ("structure", "Structure"),
+                ("mood", "Mood"),
+                ("tempo", "Tempo"),
+                ("instrumentation", "Instrumentation"),
+                ("effects", "Effects"),
+                ("additional", "Additional Notes"),
+            ]
+            for key, label in field_order:
+                if key in self.prompt_structure and self.prompt_structure[key]:
+                    parts.append(f"**{label}:** {self.prompt_structure[key]}")
+            return "\n\n".join(parts)
+        return self.prompt
+
 class GenerateResponse(BaseModel):
     id: str
     status: str
@@ -57,6 +78,9 @@ class Clip(BaseModel):
     status: str
     error_message: Optional[str] = None
     created_at: datetime
+    prompt_structure: Optional[dict] = None
+    bpm: Optional[float] = None
+    key: Optional[str] = None
 
 class RenameRequest(BaseModel):
     title: str