dashboard: new S3TT1NGS tab housing the notification toggle (closes #763)

Adds a fifth tab (◆ S3TT1NGS ◆) at the end of the dashboard tab
strip; moves the browser-notification controls out of the chrome
header into the new pane.

### Why

The chrome was carrying the notification controls as 'always-on
ergonomics' but the surface they belong on is operator preferences,
not navigation. With #589 / #701 likely adding more per-browser
preferences later (theme / density / etc.), having a dedicated
S3TT1NGS pane gives them a home so the chrome strip doesn't keep
accreting controls.

### Shape

- index.html: new `#tab-pane-settings` section with H2 + intro +
  H3 'browser notifications' group; same notif-row DOM (same IDs)
  migrated from the chrome
- flow.html: drops the duplicated notif-row from its chrome (FL0W
  reused the dashboard's strip); adds a `◆ S3TT1NGS ◆ →`
  cross-page link to `/#settings`. Notifications still fire on
  FL0W when enabled — NOTIF.show() reads
  Notification.permission + the hyperhive.notify.muted localStorage
  key directly, no buttons needed in the page DOM.
- tabs.js: adds 'settings' to TABS array so hash routing activates
  the pane
- dashboard.css: drops the chrome-anchoring `.tabbar #notif-row`
  rule and the flow-page reuse comment, both obsolete; the general
  `.notif-row` styling stays
- docs/web-ui.md: new `### S3TT1NGS tab` section; Chrome-header
  bullet drops 'Notification controls' + adds S3TT1NGS; Browser
  notifications section pointers at the new pane

### No JS or backend changes

Same IDs (notif-row, notif-enable, notif-mute, notif-unmute,
notif-status) so `NOTIF.bind()` in common.js wires the new pane
unchanged. NOTIF.show() dispatch is DOM-independent.

### Validation

`npm run --workspace @hive/dashboard build` clean (tabs.js 167.8kb,
flow.js 37.4kb, dashboard.css 50.2kb).

docs/web-ui.md

@@ -284,20 +284,22 @@ cross-page link (`◆ FL0W ◆ →`), not a pane swap.
 **Chrome header** (fixed, overlays the active tab pane):
 - **Tab strip**: `◆ SW4RM ◆`, `◆ Y3R C4LL ◆`, `◆ SYST3M ◆`,
   `◆ SCH3DUL3S ◆`, `◆ M4TR1X ◆ →` (optional page link, see below),
-  and `◆ FL0W ◆ →` (page link). 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). The M4TR1X → entry is hidden when
+  `◆ 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); S3TT1NGS has 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
   `state.matrix_gui_enabled` from `/api/state`.
-- **Notification controls**: `🔔 enable notifications` when
-  permission ungranted; `🔕 mute / 🔔 unmute` toggle once granted.
-  Always visible in the chrome regardless of active tab.
 - **Banner-thin** (`░▒▓█▓▒░ HYPERHIVE / HIVE-C0RE / WE ARE THE WIRED ░▒▓█▓▒░`)
   — sits below the tab strip.
 
+The FL0W page reuses the same chrome strip but its `◆ S3TT1NGS ◆ →`
+entry is a cross-page link back to the dashboard
+(`/#settings`) since the settings pane only lives there.
+
 ### SW4RM tab
 
 **C0NTAINERS** — live containers rendered as a depth-first
@@ -445,6 +447,32 @@ button hard-deletes (`POST /cancel-reminder/{id}`) and a
 Lives in the SCH3DUL3S tab alongside operator schedules so the
 operator has one place for everything time-fired.
 
+### S3TT1NGS tab
+
+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
+under the same `<section id="tab-pane-settings">`.
+
+**◇ browser notifications** — `🔔 enable notifications` button when
+permission ungranted; `🔕 mute / 🔔 unmute` toggle once granted
+(mute silences the dispatch without revoking the OS-level
+permission). On unsupported origins (non-secure context, or
+browsers without the `Notification` API) the controls hide and a
+single status line explains why. See `### Browser notifications`
+below for the dispatch model + the three signals the dashboard
+emits OS notifications on.
+
+The FL0W page does NOT host this pane — its tab-strip
+`◆ S3TT1NGS ◆ →` entry is a cross-page link to the dashboard's
+`#settings` route. Notifications still fire on the FL0W page when
+they're enabled here, because `NOTIF.show()` in
+`common.js` depends on `Notification.permission` + the
+`hyperhive.notify.muted` localStorage key, not on the buttons
+existing in the page DOM.
+
 ### M4TR1X page (`/matrix/`, optional)
 
 A static matrix web client (default `pkgs.fluffychat-web` rebuilt
@@ -755,6 +783,10 @@ Pure frontend (`Notification` API). Three signals trigger them:
 - new pending operator question (per id)
 - new broker message sent `to: "operator"` (live via SSE)
 
+The toggle controls live in the `S3TT1NGS` tab (`#settings`); see
+that section above for the user-facing shape. Dispatch logic lives
+in `common.js::NOTIF`.
+
 First `/api/state` after page load seeds "seen" sets without
 firing — only items that arrive while the page is open count.
 Per-event tags (`hyperhive:approval:<id>`, `hyperhive:question:<id>`,
@@ -762,12 +794,13 @@ Per-event tags (`hyperhive:approval:<id>`, `hyperhive:question:<id>`,
 notification center instead of overwriting each other.
 `console.debug` logs at every block point (unsupported,
 permission ungranted, muted) for in-browser debugging. Click
-focuses the dashboard tab. localStorage-backed mute toggle
-silences without revoking the OS permission. Requires a secure
-context (HTTPS or localhost); on other origins the controls hide
-themselves. Browsers typically suppress notifications while the
-originating tab is focused — that's a browser-level decision,
-not ours.
+focuses the dashboard tab. The localStorage key
+`hyperhive.notify.muted` (`"1"` = muted, absent = unmuted) backs
+the toggle and silences dispatch without revoking the OS
+permission. Requires a secure context (HTTPS or localhost); on
+other origins the controls hide themselves. Browsers typically
+suppress notifications while the originating tab is focused —
+that's a browser-level decision, not ours.
 
 ### Dashboard endpoints