refactor(fe): trim impl-history and duplicated-docs prose from comments

Remove or shorten comment blocks that:
- explain where code used to live (impl history)
- duplicate rationale already in docs/web-ui.md
- contain speculative/future-work notes

Changes:
- tabs.js: drop "SYST3M tab used to render this" history; keep badge purpose
- schedules.js: drop "used to be a card layout" history + speculative nit note
- stream-worker.js: replace 10-line problem-statement with docs pointer
  (rationale already in docs/web-ui.md SSE multiplexing section); trim
  future-work parenthetical from subscription-tracking comment
- system-sections.css: drop extraction-history prose; keep what it does
- core.css: drop move-history prose; keep what it imports and why

Part of issue cleanup per operator feedback.

frontend/packages/dashboard/src/core.css

@@ -1,21 +1,6 @@
 /* ─── /core.html — C0R3 page ───────────────────────────────────────
-   Standalone page for kept state (tombstones) and container load.
-   Same minimal-chrome pattern as /logs.html (a `← home` back-link +
-   a createTabStrip sub-tab strip; base tab + page-header styling comes
-   from @hive/shared via common.css, linked by core.html).
-
-   The section renderers (kept state, container load) emit the same
-   class names as before. Those section-internal rules live in
-   system-sections.css (shared with dashboard.css and builds.css, which
-   references `.rqe-source*` from the schedules view). The
-   `.hive-stats-table` the container-load table reuses lives in
-   common.css, linked directly by core.html. Importing just the section
-   rules keeps the C0R3 bundle small instead of dragging in all of
-   dashboard.css.
-
-   Rebuild queue + meta inputs have moved to /builds.html; the
-   `.rebuild-live-log-*` styles that used to live here have moved to
-   system-sections.css so builds.css can share them via @import. */
+   Kept state (tombstones) and container load. Section rules imported
+   from system-sections.css (shared with dashboard.css + builds.css). */
 @import "./system-sections.css";
 
 body.core-shell {

frontend/packages/dashboard/src/schedules.js

@@ -683,11 +683,7 @@ function renderScheduleRow(s, agents) {
 
   tr.append(el('td', { class: 'meta' }, s.owner));
 
-  // Body cell — truncates with ellipsis; full body + description (if
-  // any) on hover. Description used to be a separate visible block on
-  // the card layout; the table compresses it into the title to keep
-  // row height tight. Mara nit-flag candidate if she actually wants
-  // it visible in-table.
+  // Body cell — truncates with ellipsis; full body + description on hover.
   const bodyCell = el('td', { class: 'schedules-table-body-cell' });
   const bodyText = s.body || '';
   bodyCell.title = (s.description ? s.description + '\n\n' : '') + bodyText;

frontend/packages/dashboard/src/stream-worker.js

@@ -1,16 +1,6 @@
 // SharedWorker that holds ONE EventSource per stream URL and fans
 // every server-sent event out to every connected tab via MessagePort.
-//
-// Problem this solves: every dashboard / agent tab opens its own
-// `EventSource('/api/dashboard/stream')`. Browsers cap concurrent
-// connections per host (~6), and Firefox throttles / disconnects
-// background tabs when many are open. The result: tabs silently
-// drop the SSE, fall behind, and only catch up on focus.
-//
-// Centralising the connection in a SharedWorker means N tabs share
-// ONE backend EventSource regardless of focus state — way under the
-// per-host cap, immune to per-tab throttling, and the worker survives
-// any individual tab being suspended.
+// Design rationale: docs/web-ui.md (SSE multiplexing paragraph).
 //
 // Wire protocol (port.postMessage payloads):
 //
@@ -42,8 +32,7 @@
 //                                       signal to the client).
 //
 // Subscriptions are tracked per (port, url): a single port can
-// subscribe to multiple URLs (today only one is in use but the shape
-// stays open for the per-agent /events/stream multiplexing follow-up).
+// subscribe to multiple URLs (only one is in use today).
 // Unsubscribing the last port for a URL closes the EventSource so we
 // don't keep idle streams open.
 

frontend/packages/dashboard/src/system-sections.css

@@ -1,22 +1,7 @@
 /* ─── SYST3M/BU1LDS section panels — shared by dashboard, /core.html,
    and /builds.html ──────────────────────────────────────────────────
-   The rebuild queue, meta inputs, kept state, and container-load panels
-   render on /core.html; rebuild queue + meta inputs + live-log also
-   render on /builds.html (the build lifecycle hub). These
-   section-internal rules used to live in dashboard.css and were pulled
-   in by /core.html via a wholesale `@import "./dashboard.css"`, which
-   dragged the entire ~39kb dashboard stylesheet into the bundle.
-
-   They now live here and are `@import`ed by core.css, dashboard.css,
-   and builds.css. Each page gets only this small file instead of all
-   of dashboard.css; the dashboard keeps the rules (a couple are still
-   referenced from dashboard JS — `.rqe-source*` by the schedules view,
-   and `.hive-stats-table`, which already lives in common.css and is
-   loaded by all pages). Behaviour-preserving: identical rules, same
-   custom properties from colors.css / theme.css / common.css.
-
-   The selectors here are uniquely named to these panels and are not
-   redefined elsewhere, so the cascade is unaffected by the move. */
+   Rebuild queue, meta inputs, kept state, and container-load panels.
+   Imported by core.css, dashboard.css, and builds.css. */
 
 /* ─── meta inputs panel ────────────────────────────────────────────── */
 .meta-inputs {

frontend/packages/dashboard/src/tabs.js

@@ -129,13 +129,8 @@ window.marked = marked;
     if (containersState.delete(ev.name)) renderContainersFromState();
   }
 
-  // Derived rebuild queue state — cold-loaded from
-  // `/api/state.rebuild_queue`, then mutated live by the
-  // `rebuild_queue_changed` snapshot event. The SYST3M tab that used to
-  // render this list moved to the standalone /core.html page; the
-  // dashboard keeps the STATE because it drives the "building…" /
-  // "meta-updating…" badges on the SW4RM agent cards (see
-  // inFlightOpsByAgent + docs/web-ui.md::Container row).
+  // Rebuild queue state — drives "building…" / "meta-updating…" badges on
+  // SW4RM agent cards (see inFlightOpsByAgent + docs/web-ui.md::Container row).
   let rebuildQueueState = [];
   function syncRebuildQueueFromSnapshot(s) {
     rebuildQueueState = (s.rebuild_queue || []).slice();