pcweb: do not build on windows (unless overriding)

Avoid EMFILE errors when building reflex-web on windows during CI.

reflex-web has too many pages and causes too many files to get opened during
the build, and windows seems to have a non-configurable limit for open file
handles via the C runtime.

Until we come up with a nicer solution, simply disallow windows builds. If the
override environment variable is set (like in CI runs), then we will compile a
subset of pages for testing.

pcweb/pcweb.py

@@ -1,5 +1,8 @@
 """The main Reflex website."""
 
+import os
+import sys
+
 import reflex as rx
 import reflex.components.radix.themes as rdxt
 from pcweb import styles
@@ -25,6 +28,17 @@
     ],
 )
 
+
+# XXX: The app is TOO BIG to build on Windows, so explicitly disallow it except for testing
+if sys.platform == "win32":
+    if not os.environ.get("REFLEX_WEB_WINDOWS_OVERRIDE"):
+        raise RuntimeError(
+            "reflex-web cannot be built on Windows due to EMFILE error. To build a "
+            "subset of pages for testing, set environment variable REFLEX_WEB_WINDOWS_OVERRIDE."
+        )
+    routes = routes[:150]
+
+
 # Add the pages to the app.
 for route in routes:
     app.add_page(