ops: fix data/ triple-duplication costing ~24 GB on VPS

astro build resolves the public/data symlink and copies all activity JSON
into dist/; rsync then copied that to the webroot — but nginx already serves
/data/ directly from /var/bincio/data/ via alias, so both copies were dead
weight. Freed 36 GB → 14 GB on the live server.

- post-receive hook: prune dist/data/ before rsync, add --exclude=data/
- docs: update manual rebuild command and nginx comment to match
- serve/server.py: _mb() now uses lstat() to count symlinks at face value
  rather than following them to targets, so admin storage panel no longer
  double-counts _merged/ (which is mostly symlinks into activities/)

bincio/serve/server.py

@@ -594,7 +594,9 @@ async def admin_disk(bincio_session: Optional[str] = Cookie(default=None)) -> JS
     def _mb(path: Path) -> float:
         if not path.exists():
             return 0.0
-        total = sum(f.stat().st_size for f in path.rglob("*") if f.is_file())
+        # Use lstat to count symlink entries (few bytes each) rather than following
+        # the link to the target — prevents _merged/ from double-counting activities/.
+        total = sum(f.lstat().st_size for f in path.rglob("*") if f.is_file() or f.is_symlink())
         return round(total / 1_048_576, 1)
 
     def _count(path: Path, pattern: str = "*") -> int:
@@ -991,7 +993,7 @@ async def me_storage(bincio_session: Optional[str] = Cookie(default=None)) -> JS
     def _mb(path: Path) -> float:
         if not path.exists():
             return 0.0
-        total = sum(f.stat().st_size for f in path.rglob("*") if f.is_file())
+        total = sum(f.lstat().st_size for f in path.rglob("*") if f.is_file() or f.is_symlink())
         return round(total / 1_048_576, 2)
 
     def _count(path: Path, pattern: str = "*") -> int: