chore(frontend): scrub pre-existing issue-tag refs from source comments

The no-issue-tags-in-code rule (knowledge/hive-rules.md) was enforced on
recent PRs but several pre-existing parenthetical refs remained in the
frontend source. Replace them with plain prose — issue numbers are opaque
in source, and prose survives repo migrations + doesn't confuse static
analysis. Comment-only; no behaviour change.

- tabs.js: 4× operator-inbox refs → prose
- flow.js / flow.css: agent-filter + sent/delivered-collapse refs → prose
- home.js / home.css: H0M3 page-script + page-chrome refs → prose
- dashboard.html: 1NB0X inbox ref → prose

Closes #1549.

frontend/packages/dashboard/src/home.css

@@ -1,7 +1,7 @@
-/* H0M3 — the menu-hub page (#1464). Minimal portal styling: a banner
+/* H0M3 — the menu-hub page. Minimal portal styling: a banner
    + a responsive grid of link tiles. Colours come from theme.css (the
    shared palette); base typography from common.css. When the shared
-   page-chrome component lands (#1464 phase 2 / #1451) the banner + tile
+   page-chrome component lands (a later refactor step) the banner + tile
    styling can fold into it. */
 
 body.home-shell {