Fix: don't copy 9 GB data dir into dist/ during production builds

BINCIO_DATA_DIR is already set in the build env, so manifest.ts reads
the data root directly at build time without needing public/data.
Moving _link_data() into the serve-only branch prevents Astro from
following the symlink and copying the full data dir into dist/. Any
leftover symlink from a previous dev session is removed before build.
Dev mode is unchanged.

bincio/render/cli.py

@@ -201,15 +201,23 @@ def render(
         return
 
     _ensure_npm(site)
-    _link_data(site, data)
 
     env = {**os.environ, "BINCIO_DATA_DIR": str(data)}
 
     if serve:
+        # Dev server needs to serve /data/ files at runtime from public/
+        _link_data(site, data)
         console.print("Starting [cyan]astro dev[/cyan]…")
         subprocess.run(["npm", "run", "dev"], cwd=site, env=env)
         return
 
+    # Production build: BINCIO_DATA_DIR is already set so manifest.ts reads
+    # data directly; remove any leftover public/data symlink so Astro doesn't
+    # copy the full data directory (9+ GB) into dist/.
+    public_data = site / "public" / "data"
+    if public_data.is_symlink():
+        public_data.unlink()
+
     # Build
     cmd = ["npm", "run", "build"]
     if out_dir: