Fix settings 500: add missing block_id to FXBlock, rebuild UI

- FXBlock was missing block_id field (and __post_init__ auto-generator)
  causing AttributeError on /settings and /api/presets endpoints.
- Rebuilt Helix Vite UI from ui/ source (index-jhtO2NOz.js,
  index-D3aC6klh.css). Replaces older dist files.

src/presets/types.py

@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+import datetime
+import hashlib
 import enum
 from dataclasses import dataclass, field
 from typing import Optional
@@ -92,6 +94,13 @@ class FXBlock:
     subtype: str = ""               # Algorithm variant (e.g. "hall"/"spring"/"plate" for reverb)
     nam_model_path: str = ""        # Path to .nam file (for NAM_AMP type)
     ir_file_path: str = ""          # Path to .wav IR file (for IR_CAB type)
+    block_id: str = ""              # Unique instance ID within a chain (auto-filled if empty)
+
+    def __post_init__(self) -> None:
+        """Auto-generate block_id if empty."""
+        if not self.block_id:
+            raw = f"{self.fx_type.value}_{datetime.datetime.now(datetime.timezone.utc).timestamp()}_{id(self)}"
+            self.block_id = hashlib.md5(raw.encode()).hexdigest()[:12]
 
 
 @dataclass