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.

docs/web-ui/dashboard.md

@@ -18,9 +18,9 @@ swap.
   `◆ P33RS ◆` (hidden when `swarm.peers` is empty),
   `◆ M4TR1X ◆ →` (optional page link, see below), `◆ FL0W ◆ →`
   (page link), and `◆ S3TT1NGS ◆`. Count pills on SW4RM (container
-  count), Y3R C4LL (pending approvals + questions), and SCH3DUL3S
-  (active schedules); FL0W pill mirrors the operator inbox length
-  (hidden when zero); P33RS and S3TT1NGS have no count. The M4TR1X →
+  count), Y3R C4LL (pending approvals + questions + unread operator
+  messages), and SCH3DUL3S (active schedules); P33RS and S3TT1NGS
+  have no count. The M4TR1X →
   entry is hidden when `services.hyperhive.matrix.gui.enable` is off
   (defaults to `matrix.enable`) so operators without the matrix GUI
   on don't see a dead link — tabs.js gates the `hidden` attribute on
@@ -368,7 +368,7 @@ Operator-local preferences. State lives in the browser's
 `localStorage` — preferences do NOT sync between devices and
 do NOT survive a profile wipe. Today the tab holds one section
 (browser notifications); future preferences (theme, density,
-inbox-pill threshold, etc.) land here as sibling `<h3>` blocks
+etc.) land here as sibling `<h3>` blocks
 under the same `<section id="tab-pane-settings">`.
 
 **◇ browser notifications** — `🔔 enable notifications` button when
@@ -415,11 +415,9 @@ as the dashboard so the tab strip remains visible; SW4RM / Y3R
 C4LL / SYST3M / SCH3DUL3S are cross-page links back to `/#<tab>`,
 and the FL0W entry is marked active (`aria-current="page"`).
 
-**0PER4T0R 1NB0X** — recent messages addressed to `operator`,
-derived client-side from the dashboard event stream. Cold load
-seeds from `/dashboard/history`'s 200-message backfill; subsequent
-`sent` events with `to == "operator"` are appended live. Cap 50,
-newest-first.
+The operator inbox is **not** on this page — it lives on the
+dashboard's Y3R C4LL tab (◆ 1NB0X ◆ section, with per-message and
+mark-all read). FL0W stays the pure event firehose.
 
 **MESS4GE FL0W** — live broker tail wrapped in a `.terminal-wrap`.
 Cold load backfills the last ~200 messages from `/dashboard/history`;
@@ -437,8 +435,7 @@ terminal-style compose box: `@name` picks the recipient (sticky via
 localStorage; auto-complete from the live container list, Tab/Enter
 to confirm; `@*` broadcasts). `POST /op-send` drops
 `{from:"operator", to, body}` into the broker; the resulting SSE
-frame re-renders both the terminal row and the inbox section.
-Manager is addressed as `@root`.
+frame re-renders the terminal row. Manager is addressed as `@root`.
 
 ## L0GS page (`/logs.html`)
 
@@ -805,9 +802,8 @@ that's a browser-level decision, not ours.
 - `POST /op-send` (`to=<name>`, `body=<text>`) — drop an
   operator-authored message into `<name>`'s inbox. `to=*` fans
   out to every registered agent. Returns 200; the broker
-  `Sent` event re-renders both the message-flow terminal and
-  the operator inbox without a snapshot refetch. Used by the
-  compose textbox under MESS4GE FL0W.
+  `Sent` event re-renders the message-flow terminal without a
+  snapshot refetch. Used by the compose textbox under MESS4GE FL0W.
 - `GET /api/build-logs/{agent}?limit=N` — most-recent build log
   headers for one agent, newest first. Returns
   `Vec<BuildLogHeader>` (JSON): `id`, `agent`, `kind`, `cmdline`,