fix(dashboard): mobile rendering for resizable modals

The Settings, Workflow Steps, Automations (and friends) modals all carried
desktop `min-width: 480-520px` constraints from the resize work. On phones
that pushed them off-screen, and the overlay's 10vh top padding plus a
fractional `height: 80vh` left awkward gaps top and bottom.

Apply the same `@media (max-width: 768px)` full-screen-sheet treatment
that File Browser already had to every resize-aware modal: drop the
overlay padding, set width/height to `100vw`/`100dvh`, zero out the
min-* / max-* constraints, and disable `resize` (touchscreens can't grab
the corner grip anyway).

Also tightened the existing File Browser and GitHub Import overrides to
match (`min-width: 0`, `min-height: 0`, `resize: none`).

For TaskDetailModal the mobile rules go inside the existing first
`@media (max-width: 768px)` block to keep the FN-1331 detail-body
padding regression test happy (it captures from the first 768px media
query greedily).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/SettingsModal.css

@@ -68,6 +68,32 @@
   resize: both;
 }
 
+/* Mobile: full-screen sheet. The desktop `min-width: 520px` was forcing the
+   modal wider than narrow viewports, pushing it off-screen; the desktop
+   `height: 80vh` left awkward strips of overlay above and below. Drop the
+   overlay's default top padding so the modal actually fills the viewport,
+   and disable resize (touchscreen users can't drag the grip anyway). */
+@media (max-width: 768px) {
+  .modal-overlay:has(.settings-modal) {
+    padding-top: 0;
+    align-items: stretch;
+    justify-content: stretch;
+  }
+
+  .modal.settings-modal {
+    width: 100vw;
+    min-width: 0;
+    max-width: 100vw;
+    height: 100dvh;
+    min-height: 0;
+    max-height: 100dvh;
+    margin: 0;
+    border: none;
+    border-radius: 0;
+    resize: none;
+  }
+}
+
 /* === Settings Layout === */
 .settings-modal-heading {
   display: flex;