Doc audit: fix all broken links + correct stale facts across the KB

Fanned out 5 read-only doc-auditor subagents (one per service group) that
fact-checked the knowledge base against the live system + repo config,
researched official setup docs online, and verified progress. Applied:
- All 34 broken links fixed (real pages / external URLs / correct relative
  paths); 0 broken links remain. No .AGENTTRASH links (the 4 mentions are
  accurate descriptive text, not links).
- Fact-check fixes: Readarr retired (May 2026), Radarr v4->v6, Calibre
  9.2.1 live, Calibre-Web 0.6.25 live, Copyparty v1.20.21, LLM index
  ncmoe 38 + 786432 ctx, frank-default-small active (not frank-pp-worker),
  Hermes/SearXNG/Grafana hostnames, Loki/Alloy local images, Observability
  diagram (Promtail->Alloy), VLLM retired note, DFlash status, benchmark
  live-drift notes, Homepage test count 116.

docs/Infrastructure/Homepage Design Grilling.md

@@ -72,7 +72,7 @@ These are the deltas from the initial recommendations. Everything else was accep
 ## Build status — complete (2026-08-23)
 
 The build is done, slice by slice, full TDD (each slice red → green, committed
-and pushed). 112 tests pass. The render logic is verified with a Node DOM shim.
+and pushed). 116 tests pass. The render logic is verified with a Node DOM shim.
 
 ```mermaid
 flowchart LR