feat(pwa): installable PWA + responsive mobile dashboard

- Add Web App Manifest + ArbPulse icons (192/512/maskable/apple-touch) under
  web/public/; no service worker (real-time honesty: never serve stale data).
- Add mobile/install metadata to index.html (theme-color, viewport-fit=cover,
  apple-mobile-web-app-*, manifest + apple-touch-icon links).
- Responsive layout: PriceMatrix stacked per-venue cards below sm, StatsBar
  reflow, ~44px touch targets in Controls/ConfigPanel, safe-area top inset.
- scripts/gen-icons.ps1 derives icon sizes from the master (no new deps).
- openspec: add-pwa-mobile change (proposal/design/specs/tasks).

Co-authored-by: Cursor <cursoragent@cursor.com>

openspec/changes/add-pwa-mobile/specs/pwa/spec.md

@@ -0,0 +1,58 @@
+## ADDED Requirements
+
+### Requirement: Installable to the home screen
+The dashboard SHALL be installable to a device home screen via a Web App Manifest
+served over HTTPS, without requiring a service worker.
+
+#### Scenario: Manifest is present and valid
+- **WHEN** the dashboard is loaded over HTTPS
+- **THEN** a linked `manifest.webmanifest` is served that includes `name`,
+  `short_name`, `start_url` in scope, `display: standalone`, `theme_color`,
+  `background_color`, and at least 192px and 512px PNG icons
+
+#### Scenario: User installs from the browser
+- **WHEN** a user chooses "Install app" / "Add to Home Screen" from the browser menu
+- **THEN** the app is added with the ArbPulse icon and launches in a standalone,
+  full-window mode at `start_url`
+
+### Requirement: No offline mode and no stale data
+The app SHALL NOT register a service worker and SHALL NOT cache market data, so it
+never presents stale or fake data (real-time honesty rule).
+
+#### Scenario: No service worker is registered
+- **WHEN** the dashboard runs in any environment
+- **THEN** no service worker is registered and no application cache stores `/api`
+  responses or the SSE stream
+
+#### Scenario: Disconnected device shows a clear non-data state
+- **WHEN** the device has no working connection to the engine
+- **THEN** the UI shows its reconnecting/offline indicator and does not display
+  cached market figures as if they were live
+
+### Requirement: Responsive mobile layout
+The dashboard SHALL be usable on phone-sized viewports (~360–430px wide) without
+horizontal overflow of primary widgets, while the desktop layout is unchanged.
+
+#### Scenario: Order book fits a phone screen
+- **WHEN** the viewport is narrower than the `sm` breakpoint
+- **THEN** the order-book (`PriceMatrix`) is presented as per-venue stacked cards
+  showing bid, ask, quantities, and spread without horizontal scrolling
+
+#### Scenario: Stats and controls remain readable and tappable
+- **WHEN** the dashboard is viewed on a phone
+- **THEN** the stats bar reflows without clipping and interactive controls have
+  touch targets of at least ~44px
+
+#### Scenario: Desktop layout is preserved
+- **WHEN** the viewport is at the `lg` breakpoint or wider
+- **THEN** the existing multi-column layout and table order book render as before
+
+### Requirement: Mobile and install metadata
+The `index.html` head SHALL include the metadata needed for correct mobile rendering
+and home-screen installation on Android and iOS.
+
+#### Scenario: Head includes mobile/install tags
+- **WHEN** the page is served
+- **THEN** the head contains a `theme-color`, `viewport-fit=cover` in the viewport
+  meta, a link to the manifest, an `apple-touch-icon`, and the
+  `apple-mobile-web-app-*` tags for standalone iOS launch