feat: find-nearby skill and Telegram location support

Adds a 'find-nearby' skill for discovering nearby places using
OpenStreetMap (Overpass + Nominatim). No API keys needed. Works with:
- Coordinates (from Telegram location pins)
- Addresses, cities, zip codes, landmarks (auto-geocoded)
- Multiple place types (restaurant, cafe, bar, pharmacy, etc.)

Returns names, distances, cuisine, hours, addresses, and Google Maps
links (pin + directions). 184-line stdlib-only script.

Also adds Telegram location message handling:
- New MessageType.LOCATION in gateway base
- Telegram adapter handles LOCATION and VENUE messages
- Injects lat/lon coordinates into conversation context
- Prompts agent to ask what the user wants nearby

Inspired by PR #422 (reimplemented with simpler script and broader
skill scope — addresses/cities/zips, not just Telegram coordinates).

gateway/platforms/base.py

@@ -252,6 +252,7 @@ def cleanup_document_cache(max_age_hours: int = 24) -> int:
 class MessageType(Enum):
     """Types of incoming messages."""
     TEXT = "text"
+    LOCATION = "location"
     PHOTO = "photo"
     VIDEO = "video"
     AUDIO = "audio"