Docs: public copy, site presentation, release-gate review (D533, D534)

Public-copy language pass, homepage restructure and Documentation rename,
404 page, dead-anchor and permalink fixes, release-gate sign-off, and the
pre-release review fixes of the 2026-10-05 batch (probe-doc drift,
build-path hygiene, verify.sh and capture safety).

Refs: D533 D534

.github/SECURITY.md

@@ -12,7 +12,7 @@ surface is:
 
 A full walkthrough of what a release actually installs on your machine, and
 what a from-source build pulls in, is in
-[`docs/security-and-fidelity-status.md`](../docs/security-and-fidelity-status.md).
+[`docs/security.md`](../docs/security.md).
 
 ### Why the binaries are unsigned