chore: scrub #NNN issue references from code comments and nix descriptions

Part of the docs-migration chore (issue #708). Remove GitHub issue
numbers from inline comments, option descriptions, and rustdoc —
these are contextless noise for anyone reading the code without
access to the original discussions. Replace with prose that captures
the same rationale directly.

No functional change. Build still clean (cargo check passes).

frontend/packages/dashboard/src/tabs.js

@@ -475,7 +475,7 @@ window.marked = marked;
     // `/agent/<name>/` URLs instead of the direct `http://<host>:<port>/`
     // TCP fallback — the gateway proxies the prefix to the per-agent
     // harness (TCP via `agent-ports.json` or unix-domain via
-    // `agent-sockets.json` per #784 / #815). See
+    // `agent-sockets.json`). See
     // `docs/web-ui.md::Container row` + `docs/gateway.md::Vhost map`.
     const gatewayLinks = !!(s && s.gateway_enabled);
     const ul = el('ul', { class: 'containers' });