fix(a11y): 36 modal dialogs announce themselves and take focus (#185)

Most modals rendered a folds Dialog/Modal with no role and no name, and
their focus traps used `initialFocus: false`, so focus stayed behind the
modal and a screen reader never announced it.

- 32 dialogs with a visible heading: role="dialog", aria-modal,
  aria-labelledby → the heading (given an id), tabIndex=-1.
- 4 dialogs that already had a name (Leave Room, room topic viewer,
  server ACL, room-nav prompt): role + aria-modal.
- Their focus traps drop `initialFocus: false` for focus-trap's default
  (keep an already-focused autoFocus field, else the first tabbable
  element) with the dialog itself as fallbackFocus, so a dialog without
  a tabbable node can't crash the trap. Traps that live in a parent
  (UIA stages, Logout, Forward, Invite) get the semantics only.
- The file drop overlay is deliberately left alone (not a dialog).

Checked at runtime: Join with Address, Delete Message, Report Message,
Leave Room and Logout open as named dialogs with focus inside and close
with Escape (Tab first when a text field has focus — the shared
stopPropagation keeps Escape from discarding typed text, by design).
The axe e2e spec (6 tests) passes; eslint warnings unchanged (46).
17 modals with no heading (image/file viewers, loading screens) remain.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/DeviceVerificationSetup.tsx

@@ -293,7 +293,15 @@ export const DeviceVerificationSetup = forwardRef<HTMLDivElement, DeviceVerifica
     const modalStyle = useModalStyle(480);
 
     return (
-      <Dialog ref={ref} style={modalStyle}>
+      <Dialog
+        id="deviceverificationsetup-dialog-1"
+        role="dialog"
+        aria-modal="true"
+        aria-labelledby="deviceverificationsetup-dialog-1-title"
+        tabIndex={-1}
+        ref={ref}
+        style={modalStyle}
+      >
         <Header
           style={{
             padding: `0 ${config.space.S200} 0 ${config.space.S400}`,
@@ -303,7 +311,7 @@ export const DeviceVerificationSetup = forwardRef<HTMLDivElement, DeviceVerifica
           size="500"
         >
           <Box grow="Yes">
-            <Text as="h2" size="H4">
+            <Text id="deviceverificationsetup-dialog-1-title" as="h2" size="H4">
               Setup Device Verification
             </Text>
           </Box>
@@ -331,7 +339,15 @@ export const DeviceVerificationReset = forwardRef<HTMLDivElement, DeviceVerifica
     const modalStyle = useModalStyle(480);
 
     return (
-      <Dialog ref={ref} style={modalStyle}>
+      <Dialog
+        id="deviceverificationsetup-dialog-2"
+        role="dialog"
+        aria-modal="true"
+        aria-labelledby="deviceverificationsetup-dialog-2-title"
+        tabIndex={-1}
+        ref={ref}
+        style={modalStyle}
+      >
         <Header
           style={{
             padding: `0 ${config.space.S200} 0 ${config.space.S400}`,
@@ -341,7 +357,7 @@ export const DeviceVerificationReset = forwardRef<HTMLDivElement, DeviceVerifica
           size="500"
         >
           <Box grow="Yes">
-            <Text as="h2" size="H4">
+            <Text id="deviceverificationsetup-dialog-2-title" as="h2" size="H4">
               Reset Device Verification
             </Text>
           </Box>