refactor(documents): fully decouple document stack from server startup; Windows-safe tests

Addresses round-1 review on #878:

- Move the eager `document_processors` imports out of the API startup graph:
  `app.py` (get_registry now imported inside initialize_document_processors,
  after the disabled early-return) and `vector/processor.py` (get_registry now
  imported at its single use site). Importing `app` + `cli` no longer loads
  `document_processors` / `_isolation` at all -- the #877 stack is fully out of
  startup (pymupdf still loads via search/pdf_highlighter, a Windows-compatible
  and separately-tracked concern).
- Make `tests/unit/test_pdf_parse_isolation.py` importable on Windows: guard the
  top-level `import resource` with try/except and skip the three rlimit
  computation tests via a `requires_resource` marker when the module is absent.
  The Windows no-op / import-guard tests don't use the real module and still run.
- Fix the `# pragma: no cover` comment on the win32 branch to be accurate.
- Add `enable-cache: true` to the package-smoke setup-uv step.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/test_pdf_parse_isolation.py

@@ -13,7 +13,6 @@ check on the sample PDFs, not here (unit tests must not spawn the heavy worker
 or depend on the sample files).
 """
 
-import resource
 import sys
 
 import anyio
@@ -28,8 +27,20 @@ from nextcloud_mcp_server.document_processors._isolation import (
     run_isolated_pdf_parse,
 )
 
+# ``resource`` is a Unix-only stdlib module (absent on Windows, #877). Guard the
+# import so this test module stays importable on Windows; the rlimit-computation
+# tests below are skipped there via the ``requires_resource`` marker.
+try:
+    import resource
+except ImportError:  # pragma: no cover - only reached on Windows
+    resource = None  # type: ignore[assignment]
+
 pytestmark = pytest.mark.unit
 
+requires_resource = pytest.mark.skipif(
+    resource is None, reason="resource module is Unix-only (absent on Windows)"
+)
+
 
 def _tiny_pdf() -> bytes:
     doc = pymupdf.open()
@@ -112,6 +123,7 @@ async def test_timeout_kills_and_classifies_as_timeout(monkeypatch):
 # --- _apply_mem_limit computation (mocked; never applied to the test proc) ---
 
 
+@requires_resource
 def test_apply_mem_limit_caps_soft_below_finite_hard(monkeypatch):
     captured = {}
     monkeypatch.setattr(_isolation, "_MEM_LIMIT_APPLIED", False)
@@ -130,6 +142,7 @@ def test_apply_mem_limit_caps_soft_below_finite_hard(monkeypatch):
     assert hard == 4 * 1024**3
 
 
+@requires_resource
 def test_apply_mem_limit_uses_target_when_hard_unlimited(monkeypatch):
     captured = {}
     monkeypatch.setattr(_isolation, "_MEM_LIMIT_APPLIED", False)
@@ -148,6 +161,7 @@ def test_apply_mem_limit_uses_target_when_hard_unlimited(monkeypatch):
     assert hard == resource.RLIM_INFINITY
 
 
+@requires_resource
 def test_apply_mem_limit_is_applied_once(monkeypatch):
     calls = []
     monkeypatch.setattr(_isolation, "_MEM_LIMIT_APPLIED", False)