feat: Settings modal with danger zone admin operations

Backend:
- POST /api/admin/clear-waveforms — deletes all cached waveform SVGs
- POST /api/admin/delete-all-clips — nuclear option: deletes all clips,
  MP3s, artwork, and waveforms. Returns deleted count.
- database.py: delete_all_clips() for bulk DB wipe
- Clip deletion cascade-removes waveform SVGs

Frontend:
- SettingsModal.tsx: center-stage modal with backdrop blur (bg-black/60
  backdrop-blur-sm). Danger zone with red-styled border and header.
- Two-step confirmation for Delete All (click once to arm, click again
  to confirm). Shows clip count dynamically.
- Gear icon trigger in header bar
- App.tsx: handleClearWaveforms + handleDeleteAll handlers

Docs:
- Architecture KB updated with album art, waveform, settings modal sections
- Tasks KB updated with T-021 (waveform) and TASK-001 (album art) marked done
- T-026 (settings modal) added to backlog

backend/src/database.py

@@ -151,4 +151,9 @@ async def remove_artwork(clip_id: str):
 async def delete_clip(clip_id: str):
     async with aiosqlite.connect(DB_PATH) as db:
         await db.execute("DELETE FROM clips WHERE id = ?", (clip_id,))
+        await db.commit()
+
+async def delete_all_clips():
+    async with aiosqlite.connect(DB_PATH) as db:
+        await db.execute("DELETE FROM clips")
         await db.commit()

backend/src/main.py

@@ -10,7 +10,7 @@ from dotenv import load_dotenv
 load_dotenv(Path(__file__).parent.parent / ".env")
 
 from models import GenerateRequest, GenerateResponse, ClipList, RenameRequest, LYRIA_MODELS, DEFAULT_MODEL
-from database import init_db, create_clip, get_clips, get_clip, delete_clip, update_clip_status, rename_clip, set_artwork, remove_artwork
+from database import init_db, create_clip, get_clips, get_clip, delete_clip, update_clip_status, rename_clip, set_artwork, remove_artwork, delete_all_clips
 from lyria_client import generate_clip, save_clip_file
 from waveform import generate_waveform_svg, get_waveform_path
 
@@ -226,6 +226,42 @@ async def rename_clip_endpoint(clip_id: str, request: RenameRequest):
     updated = await get_clip(clip_id)
     return updated
 
+# ─── Admin Endpoints ──────────────────────────────────────────────
+
+@app.post("/api/admin/clear-waveforms")
+async def clear_waveforms():
+    """Delete all cached waveform SVGs. They regenerate on next view."""
+    from waveform import WAVEFORM_DIR
+    count = 0
+    if WAVEFORM_DIR.exists():
+        for f in WAVEFORM_DIR.glob("*.svg"):
+            f.unlink()
+            count += 1
+    return {"cleared": count}
+
+@app.post("/api/admin/delete-all-clips")
+async def delete_all_clips_endpoint():
+    """Delete all clips, MP3s, artwork, and waveforms. Nuclear option."""
+    # Get all clips to clean up files
+    all_clips = await get_clips()
+    for clip in all_clips:
+        # Delete MP3
+        mp3_path = CLIPS_DIR / clip["filename"]
+        if mp3_path.exists():
+            mp3_path.unlink()
+        # Delete artwork
+        if clip.get("artwork_filename"):
+            art_path = ARTWORK_DIR / clip["artwork_filename"]
+            if art_path.exists():
+                art_path.unlink()
+        # Delete waveform
+        wf_path = get_waveform_path(clip["id"])
+        if wf_path and wf_path.exists():
+            wf_path.unlink()
+    # Clear DB
+    await delete_all_clips()
+    return {"deleted": len(all_clips)}
+
 if __name__ == "__main__":
     import uvicorn
     uvicorn.run(app, host="0.0.0.0", port=8000)