fix: minor 4.0 issues in Android validation, docs, and docstring (#2891)

* fix: minor 4.0 issues in android validation, docs, and docstring

- android: raise a clear FatalError when ANDROID_API_LEVEL is not an
  integer, instead of an uncaught ValueError deep in localized_vars
- docs: note that delvewheel is the default Windows repair-wheel-command
  since 4.0 and how to skip it for platform-tagged wheels with no
  extension module; update the now-outdated FAQ wording
- venv: fix _parse_pip_constraint_for_virtualenv docstring to say
  marker-bearing constraints are evaluated against the host's default
  environment (not skipped) when marker_env is None

Assisted-by: ClaudeCode:claude-opus-4.8

* fix: use int() with original error for ANDROID_API_LEVEL validation

Handle ANDROID_API_LEVEL validation via try/except around int() so the
original exception message is surfaced, and so non-ASCII Unicode digits
(which isdigit() accepts but int() may reject) are handled correctly.

Assisted-by: ClaudeCode:claude-opus-4.8

* refactor: address reivew by moving error catch

Assisted-by: ClaudeCode:claude-opus-4.8
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

---------

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

docs/options.md

@@ -971,6 +971,9 @@ Default:
 A shell command to repair a built wheel by copying external library dependencies into the wheel tree and relinking them.
 The command is run on each built wheel (except for pure Python ones) before testing it.
 
+!!! note
+    Since cibuildwheel 4.0, `delvewheel` is the default `repair-wheel-command` on Windows, so extension-module DLLs are bundled automatically. If a wheel has a platform tag but contains no extension module (for example, a package that sets a platform tag but ships a pre-built DLL itself), `delvewheel` may error. In that case, set `repair-wheel-command = ""` to skip the repair step.
+
 The following placeholders must be used inside the command and will be replaced by cibuildwheel:
 
 - `{wheel}` for the absolute path to the built wheel