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/stream-worker.js

@@ -1,8 +1,7 @@
 // SharedWorker that holds ONE EventSource per stream URL and fans
 // every server-sent event out to every connected tab via MessagePort.
 //
-// Problem this solves (#448 — mara: "firefox disconnects bc of too
-// many tabs"): every dashboard / agent tab opens its own
+// Problem this solves: every dashboard / agent tab opens its own
 // `EventSource('/dashboard/stream')`. Browsers cap concurrent
 // connections per host (~6), and Firefox throttles / disconnects
 // background tabs when many are open. The result: tabs silently
@@ -29,7 +28,7 @@
 //                                       re-sync after a reconnect gap.
 //     { kind: 'message', url: '...', data: '<raw SSE data string>' }
 //     { kind: 'error',   url: '...' }   relayed from EventSource.onerror.
-//     { kind: 'ping'     }             #515: heartbeat — fired every
+//     { kind: 'ping'     }             heartbeat — fired every
 //                                       PING_INTERVAL_MS to every
 //                                       connected port. The client's
 //                                       watchdog uses these as

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' });