feat: Text generation suggestions via Gemini models

Backend:
- New text_gen.py module with Gemini text generation client
  - suggest_prompts(): generates 3 prompt suggestions from user input
  - get_text_gen_config(): loads config from .env (model, API key, safety)
  - get_available_models(): returns list of Gemini text models
  - Safety settings: harassment, hate_speech, sexually_explicit, dangerous
    Configurable via TEXT_GEN_SAFETY_* env vars (default: BLOCK_ONLY_HIGH)
- New endpoints:
  * POST /api/text-gen/suggest — generates 3 prompt suggestions
  * GET /api/text-gen/models — lists available text models
  * GET /api/text-gen/config — returns safe config (API key masked)
  * POST /api/text-gen/config — updates config in-memory
- Default model: gemini-2.5-flash
- Fallback API key: LYRIA_API_KEY if TEXT_GEN_API_KEY not set
- System prompt: expert music producer persona for rich musical detail

Frontend:
- New SuggestionsModal component for displaying generated suggestions
  - Auto-fetches when opened
  - Shows loading spinner, error state, or suggestion list
  - Each suggestion clickable to populate the prompt field
  - Hover effect: 'Click to use this prompt →'
- Generator component updated with 'Get Suggestions ✨' button
  - Appears next to prompt label in both Basic and Advanced modes
  - Disabled when no input present
  - Clicking suggestion populates the prompt/structured fields
- SettingsModal expanded with Text Generation section (collapsible)
  - Same pattern as Image Generation: model, API key status, safety filters
  - Editable dropdowns with Save Changes button
  - Refactored to use shared useGenSettings hook for both sections

Models Available:
- gemini-2.5-flash (GA, default) — best price-to-performance
- gemini-2.5-pro (GA) — highest quality reasoning
- gemini-3.5-flash (Preview) — next-gen Flash
- gemini-3.1-flash (Preview) — latest with thinking

Architecture KB and Tasks KB updated.

backend/src/main.py

@@ -14,9 +14,8 @@ from database import init_db, create_clip, get_clips, get_clip, delete_clip, upd
 from lyria_client import generate_clip, save_clip_file
 from waveform import generate_waveform_svg, get_waveform_path
 from analysis import analyze_clip
-from image_gen import generate_artwork, get_image_gen_config, get_available_models
-from analysis import analyze_clip
 from image_gen import generate_artwork, get_image_gen_config, get_available_models, SAFETY_LEVELS
+from text_gen import suggest_prompts, get_text_gen_config, get_available_models as get_text_models
 
 app = FastAPI(title="Lyria Studio", version="0.1.0")
 
@@ -320,6 +319,55 @@ async def update_image_gen_configuration(request: dict):
     
     return {"status": "updated"}
 
+# ─── Text Generation Endpoints ──────────────────────────────────────
+
+@app.get("/api/text-gen/models")
+async def list_text_gen_models():
+    """List available text generation models."""
+    return {"models": get_text_models()}
+
+@app.get("/api/text-gen/config")
+async def get_text_gen_configuration():
+    """Get current text generation configuration (safe values only)."""
+    config = get_text_gen_config()
+    return {
+        "model": config["model"],
+        "safety_harassment": config["safety_harassment"],
+        "safety_hate_speech": config["safety_hate_speech"],
+        "safety_sexually_explicit": config["safety_sexually_explicit"],
+        "safety_dangerous": config["safety_dangerous"],
+        "has_api_key": bool(config.get("api_key")),
+    }
+
+@app.post("/api/text-gen/config")
+async def update_text_gen_configuration(request: dict):
+    """Update text generation configuration (in-memory only)."""
+    if "model" in request:
+        os.environ["TEXT_GEN_MODEL"] = request["model"]
+    if "safety_harassment" in request:
+        os.environ["TEXT_GEN_SAFETY_HARASSMENT"] = request["safety_harassment"]
+    if "safety_hate_speech" in request:
+        os.environ["TEXT_GEN_SAFETY_HATE_SPEECH"] = request["safety_hate_speech"]
+    if "safety_sexually_explicit" in request:
+        os.environ["TEXT_GEN_SAFETY_SEXUALLY_EXPLICIT"] = request["safety_sexually_explicit"]
+    if "safety_dangerous" in request:
+        os.environ["TEXT_GEN_SAFETY_DANGEROUS"] = request["safety_dangerous"]
+    return {"status": "updated"}
+
+@app.post("/api/text-gen/suggest")
+async def get_suggestions(request: dict):
+    """Get prompt suggestions based on user input."""
+    user_input = request.get("input", "").strip()
+    if not user_input:
+        raise HTTPException(status_code=400, detail="Input is required")
+    
+    try:
+        config = get_text_gen_config()
+        suggestions = await suggest_prompts(user_input, config=config)
+        return {"suggestions": suggestions}
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=f"Suggestion generation failed: {str(e)}")
+
 @app.patch("/api/clips/{clip_id}")
 async def rename_clip_endpoint(clip_id: str, request: RenameRequest):
     clip = await get_clip(clip_id)