fix(mobile): raise the phone breakpoint from 430px to 600px

The phone tier stopped at innerWidth < 430 and @media (max-width: 430px), so every current large phone landed in the tablet layout: the 430pt iPhone 14 Pro Max, 15 Plus, 15 Pro Max and 16 Plus, the 440pt iPhone 16 Pro Max and 17 Pro Max, Pixel 6 Pro, 7 Pro and OnePlus 12 Pro, the 448pt Pixel 8 Pro and 9 Pro XL, and the Galaxy Z Fold 5 cover screen at 460. On those devices the header icon row replaced the session pill, the toolbar kept the desktop Run Shell button instead of Enter and the mic, the keyboard accessory bar could never become visible because its .visible rule lives inside the phone block, and the toolbar jumped to the top of the page when the keyboard opened.

The new cutoff is 600, the line test/mobile/devices.ts already draws between large phones (430-599) and small tablets (600-767). No physical device sits between 480 and 600, but a phone zoomed out one or two steps in Safari does: a 440pt iPhone at 85% or 75% page zoom reports 518px or 587px and still needs the phone controls, which a 480 cutoff would have taken away. The phone block is max-width: 599px and the tablet block starts at min-width: 600px, so a 600px device is a tablet in CSS and in getDeviceType() alike instead of straddling the boundary the way 430pt phones did.

The number changes everywhere it is encoded: JS, CSS, comments, CLAUDE.md, the CI tests that pin the phone block, and the test:mobile helpers. Measurement history that names 430px stays as written.

src/web/public/styles.css

@@ -5156,7 +5156,7 @@ body.touch-device .terminal-container .xterm .xterm-helper-textarea {
 .run-mode-dot.shell { background: #94a3b8; }
 
 /* Phone-only Enter button (see index.html). Hidden by default at every width;
-   mobile.css turns it on inside @media (max-width: 430px), where it takes over
+   mobile.css turns it on inside @media (max-width: 599px), where it takes over
    the slot the Shell button occupies on wider screens. */
 .btn-toolbar.btn-enter {
   display: none;
@@ -11807,7 +11807,7 @@ kbd {
 }
 /* Footer row: the buttons are btn-toolbar (display: flex, block-level), so
    without this rule the four of them stack vertically. Mirrors the
-   runSummaryModal footer; the ≤430px block in mobile.css adds wrapping. */
+   runSummaryModal footer; the phone block (under 600px) in mobile.css adds wrapping. */
 .readmymind-modal .modal-footer {
   display: flex;
   justify-content: flex-end;
@@ -13184,7 +13184,7 @@ body.touch-device.cjk-input-visible .main {
    Keyboard Accessory Bar
    Base styles in styles.css (always loaded) so iPad landscape (≥1024px,
    where mobile.css doesn't load) still gets dark styling. Phone overrides
-   remain in mobile.css @media (max-width: 430px).
+   remain in mobile.css @media (max-width: 599px).
    ═══════════════════════════════════════════════════════════════ */
 
 .keyboard-accessory-bar {