fix(review): type timeout as float; document worker reuse + identity check

Address PR #852 round 3 (all 🟡, no blockers):

- config: DOCUMENT_PARSE_TIMEOUT_SECONDS is now float (default 120.0) so a
  fractional value is honoured rather than silently stored in an int field;
  matches anyio.move_on_after's float seconds.
- _isolation: comment that a clean rlimit MemoryError leaves the worker alive
  in anyio's pool (vs the SIGKILL/BrokenWorkerProcess path that respawns) --
  acceptable since RLIMIT_AS caps virtual address space, not RSS.
- processor: note the `if indexed is False` is a deliberate identity check --
  a successful index (incl. dedup hit) returns None and must not be mistaken
  for a parse failure.

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

nextcloud_mcp_server/config.py

@@ -134,7 +134,7 @@ _DEFAULTS: dict[str, Any] = {
     "document_chunk_overlap": 200,
     # PDF parse isolation (OOM guard)
     "document_pdf_graphics_limit": 5000,
-    "document_parse_timeout_seconds": 120,
+    "document_parse_timeout_seconds": 120.0,
     "document_parse_mem_limit_mb": 1536,
     # Observability
     "metrics_enabled": True,
@@ -716,7 +716,9 @@ class Settings:
     # >=1 -- pymupdf4llm treats 0 as "no cap", which re-exposes the OOM.
     document_pdf_graphics_limit: int = 5000
     # wall-clock cap per parse; the worker subprocess is killed on timeout.
-    document_parse_timeout_seconds: int = 120
+    # float so a fractional DOCUMENT_PARSE_TIMEOUT_SECONDS is honoured, matching
+    # anyio.move_on_after's float seconds.
+    document_parse_timeout_seconds: float = 120.0
     # RLIMIT_AS in the parse subprocess (below the pod limit). Applied once per
     # worker for its lifetime, so changing it needs a pod restart.
     document_parse_mem_limit_mb: int = 1536