F14: add per-activity delete (DELETE /api/activity/{id} + drawer button)

Server endpoint removes the activity JSON, GeoJSON, timeseries, sidecar
edit, and images directory. Also purges the dedup cache entry so the
file can be re-uploaded if needed. Runs merge_all + rebuild afterwards.

EditDrawer: two-click delete button (click once → "Confirm delete?",
click again → deletes). On success, dispatches 'deleted' event.
ActivityDetail navigates back to the feed on delete.

bincio/serve/server.py

@@ -597,6 +597,56 @@ async def post_activity(
     return JSONResponse({"ok": True})
 
 
+@app.delete("/api/activity/{activity_id}")
+async def delete_activity(
+    activity_id: str,
+    bincio_session: Optional[str] = Cookie(default=None),
+) -> JSONResponse:
+    """Delete a single activity and all associated files for the logged-in user."""
+    user = _require_user(bincio_session)
+    _check_id(activity_id)
+    dd = _get_data_dir() / user.handle
+    acts_dir = dd / "activities"
+
+    json_path = acts_dir / f"{activity_id}.json"
+    if not json_path.exists():
+        raise HTTPException(404, "Activity not found")
+
+    import shutil
+
+    # Remove the source files (activities dir)
+    for suffix in (".json", ".geojson", ".timeseries.json"):
+        p = acts_dir / f"{activity_id}{suffix}"
+        p.unlink(missing_ok=True)
+
+    # Remove sidecar edit and images
+    sidecar = dd / "edits" / f"{activity_id}.md"
+    sidecar.unlink(missing_ok=True)
+    images_dir = dd / "edits" / "images" / activity_id
+    if images_dir.exists():
+        shutil.rmtree(images_dir)
+
+    # Remove from dedup cache so the file can be re-uploaded if needed
+    cache_path = dd / ".bincio_cache.json"
+    if cache_path.exists():
+        try:
+            cache = json.loads(cache_path.read_text(encoding="utf-8"))
+            if isinstance(cache, dict) and "activities" in cache:
+                cache["activities"] = [
+                    a for a in cache["activities"] if a.get("id") != activity_id
+                ]
+                cache_path.write_text(json.dumps(cache, indent=2, ensure_ascii=False))
+        except Exception:
+            pass  # corrupt cache — leave it; next extract will rebuild
+
+    # Full merge needed: activity removed from index
+    from bincio.render.merge import merge_all
+    merge_all(dd)
+    _trigger_rebuild(user.handle)
+
+    return JSONResponse({"ok": True})
+
+
 @app.get("/api/activity/{activity_id}/images")
 async def list_images(
     activity_id: str,