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>

nextcloud_mcp_server/document_processors/_isolation.py

@@ -25,7 +25,7 @@ from anyio import BrokenWorkerProcess
 # importing it unconditionally crashed Windows startup (#877). The RLIMIT_AS cap
 # it provides is a Linux-pod safety measure, not a correctness requirement, so on
 # platforms without it we fall back to a no-op (``resource is None``).
-if sys.platform == "win32":  # pragma: no cover - exercised only on Windows
+if sys.platform == "win32":  # pragma: no cover - win32-only path
     resource = None
 else:
     import resource