UX improvements: mobile bottom sheet, cuisine taxonomy, search enhancements

- Add BottomSheet component for Google Maps-style restaurant detail on mobile
  (3-snap drag: 40%/55%/92%, velocity-based close, backdrop overlay)
- Mobile map mode now full-screen with bottom sheet overlay for details
- Collapsible filter panel on mobile with active filter badge count
- Standardized cuisine taxonomy (46 categories: 한식|국밥, 일식|스시 etc.)
  with LLM remap endpoint and admin UI button
- Enhanced search: keyword search now includes foods_mentioned + video title
- Search results include channels array for frontend filtering
- Channel filter moved to frontend filteredRestaurants (not API-level)
- LLM extraction prompt updated for pipe-delimited region + cuisine taxonomy
- Vector rebuild endpoint with rich JSON chunks per restaurant
- Geolocation-based auto region selection on page load
- Desktop filters split into two clean rows

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/core/cache.py

@@ -0,0 +1,107 @@
+"""Redis cache layer — graceful fallback when Redis is unavailable."""
+
+from __future__ import annotations
+
+import json
+import logging
+import os
+from typing import Any
+
+import redis
+
+logger = logging.getLogger(__name__)
+
+_client: redis.Redis | None = None
+_disabled = False
+
+DEFAULT_TTL = 600  # 10 minutes
+
+
+def _get_client() -> redis.Redis | None:
+    global _client, _disabled
+    if _disabled:
+        return None
+    if _client is None:
+        host = os.environ.get("REDIS_HOST", "192.168.0.147")
+        port = int(os.environ.get("REDIS_PORT", "6379"))
+        db = int(os.environ.get("REDIS_DB", "0"))
+        try:
+            _client = redis.Redis(
+                host=host, port=port, db=db,
+                socket_connect_timeout=2,
+                socket_timeout=2,
+                decode_responses=True,
+            )
+            _client.ping()
+            logger.info("Redis connected: %s:%s/%s", host, port, db)
+        except Exception as e:
+            logger.warning("Redis unavailable (%s), caching disabled", e)
+            _client = None
+            _disabled = True
+            return None
+    return _client
+
+
+def make_key(*parts: Any) -> str:
+    """Build a cache key like 'tasteby:restaurants:cuisine=한식:limit=100'."""
+    return "tasteby:" + ":".join(str(p) for p in parts if p is not None and p != "")
+
+
+def get(key: str) -> Any | None:
+    """Get cached value. Returns None on miss or error."""
+    try:
+        client = _get_client()
+        if not client:
+            return None
+        val = client.get(key)
+        if val is not None:
+            return json.loads(val)
+    except Exception as e:
+        logger.debug("Cache get error: %s", e)
+    return None
+
+
+def set(key: str, value: Any, ttl: int = DEFAULT_TTL) -> None:
+    """Cache a value as JSON with TTL."""
+    try:
+        client = _get_client()
+        if not client:
+            return
+        client.setex(key, ttl, json.dumps(value, ensure_ascii=False, default=str))
+    except Exception as e:
+        logger.debug("Cache set error: %s", e)
+
+
+def flush() -> None:
+    """Flush all tasteby cache keys."""
+    try:
+        client = _get_client()
+        if not client:
+            return
+        cursor = 0
+        while True:
+            cursor, keys = client.scan(cursor, match="tasteby:*", count=200)
+            if keys:
+                client.delete(*keys)
+            if cursor == 0:
+                break
+        logger.info("Cache flushed")
+    except Exception as e:
+        logger.debug("Cache flush error: %s", e)
+
+
+def invalidate_prefix(prefix: str) -> None:
+    """Delete all keys matching a prefix."""
+    try:
+        client = _get_client()
+        if not client:
+            return
+        cursor = 0
+        while True:
+            cursor, keys = client.scan(cursor, match=f"{prefix}*", count=200)
+            if keys:
+                client.delete(*keys)
+            if cursor == 0:
+                break
+    except Exception as e:
+        logger.debug("Cache invalidate error: %s", e)