refactor(flow): drop operator-inbox UI, now lives on Y3R C4LL (#1483)

The operator inbox moved to the dashboard's Y3R C4LL tab in #1469
(◆ 1NB0X ◆ section, with per-message + mark-all read). FL0W goes back
to being the pure event firehose, so remove its now-redundant inbox UI:

- flow.js: drop the operatorInbox store, inboxAppendFromEvent,
  buildInboxListNode, renderInbox, the inbox-pill click wiring, and the
  onAnyEvent hook that fed them. The side panel was only used for the
  inbox flyout on this page, so drop Panel.bind() + the Panel import too.
- flow.html: remove the inbox pill, the offscreen inbox-section div, and
  the side-panel markup.
- flow.css: remove the .flow-pill* and .flow-inbox-headless rules.
- home.html: Flow tile desc → "live all-agents message firehose".
- docs/web-ui/dashboard.md: drop the FL0W 0PER4T0R 1NB0X section, point
  at Y3R C4LL, and fix the count-pill + /op-send descriptions.

The agent filter, sent→delivered collapse, compose box, and OS
notifications on operator-bound traffic are unaffected.

frontend/packages/dashboard/src/flow.css

@@ -1,8 +1,7 @@
 /* ─── /flow.html — full-page chat ─────────────────────────────────
-   See docs/web-ui.md::FL0W page for the page-vs-pane rationale
-   and the inbox-flyout-as-pill ergonomics. Shape mirrors the
-   per-agent live page (frosted-glass header + composer, full-
-   viewport terminal). */
+   See docs/web-ui.md::FL0W page for the page-vs-pane rationale.
+   Shape mirrors the per-agent live page (frosted-glass header +
+   composer, full-viewport terminal). */
 
 :root {
   /* Approximate height of the flow chrome (tabbar + dashboard-chrome
@@ -59,47 +58,6 @@ body.flow-shell .tabbar .tab.active.tab-link {
   border-color: var(--purple-dim);
   box-shadow: 0 -2px 12px -4px rgba(203, 166, 247, 0.4);
 }
-/* Inbox pill — operator inbox flyout trigger. Sits right under the
-   header so it stays in the operator's gaze without crowding the
-   chat. Same shape as the agent page's header pills. */
-.flow-pill {
-  position: fixed;
-  top: calc(var(--flow-header-h) + 0.8em);
-  right: 1em;
-  z-index: 25;
-  background: var(--bg-elev);
-  border: 1px solid var(--purple-dim);
-  color: var(--fg);
-  font-family: inherit;
-  font-size: 0.85em;
-  letter-spacing: 0.04em;
-  border-radius: 999px;
-  padding: 0.3em 0.8em;
-  display: inline-flex;
-  align-items: center;
-  gap: 0.5em;
-  cursor: pointer;
-  box-shadow: 0 4px 14px rgba(0, 0, 0, 0.35);
-  transition: border-color 0.15s ease, box-shadow 0.15s ease, color 0.15s ease;
-}
-.flow-pill:hover {
-  border-color: var(--purple);
-  color: var(--purple);
-  box-shadow: 0 0 12px -2px var(--purple);
-}
-.flow-pill-icon { font-size: 1.05em; line-height: 1; }
-.flow-pill-label { color: var(--muted); }
-.flow-pill-count {
-  background: rgba(250, 179, 135, 0.18);
-  color: var(--amber);
-  border-radius: 999px;
-  padding: 0 0.5em;
-  min-width: 1.6em;
-  text-align: center;
-  font-weight: bold;
-  font-variant-numeric: tabular-nums;
-}
-
 .flow-main {
   position: absolute;
   top: 0;
@@ -159,11 +117,6 @@ body.flow-shell .flow-main-slim {
   padding: 0.4em 1em;
 }
 
-/* Hidden inbox section on the flow page — the renderInbox path
-   wants `#inbox-section` in the DOM (legacy contract), but we
-   surface the messages via the pill/flyout instead. */
-.flow-inbox-headless { display: none !important; }
-
 /* Agent filter (#1473): a select in the FL0W header narrows the
    timeline to messages involving one agent. Non-matching rows get
    `.flow-hidden`; the select reuses the journal-unit control look. */