Sign in on a phone with no console work, in the browser's own session

Mobile OAuth reused the desktop client all along; what stopped it was the
browser. Sending the user out to Safari or Chrome backgrounds the app, iOS
suspends it, and the redirect carrying the code arrives at a socket nobody
is accepting on. The consent page now opens in front of the app instead, in
SFSafariViewController or a Chrome Custom Tab, so the loopback listener
stays live and the existing `installed` client is enough. Verified against
Google's real consent screen on a simulator and an emulator.

A per-platform client is still supported and is now an upgrade rather than a
prerequisite. On iOS it buys ASWebAuthenticationSession, which shares
Safari's session so nobody is asked to sign in to Google twice. Android
needs nothing: Custom Tabs share Chrome's cookies, measured rather than
assumed. iOS session sharing could not be confirmed on the simulator and
wants a real device.

Never an app-owned WebView: Google blocks it, and rightly, since a webview
the app controls can read the password typed into it.

Cancelling is no longer reported as a failure. AuthEvent carries a
`cancelled` flag, set by comparing against the constant every back-out path
returns, and Google's `access_denied` on desktop counts too.

Five frontend bugs found by driving the real UI, not by reading it: the
details card slid under the tab bar leaving its buttons unhittable; the
ghost click after a touch pressed a button in the card that tap had just
opened, opening the editor by itself; the swipe that pages the day was dead
over every read-only block; 84px of macOS traffic-light lane was reserved on
platforms with no traffic lights; and the desktop header ignored the top
safe area on an iPad. A first launch now says what to do next rather than
showing an empty grid, and accounts are named as Google accounts throughout.

src-tauri/Cargo.toml

@@ -44,9 +44,10 @@ chacha20poly1305 = "0.10"
 tauri-plugin-process = "2"
 tauri-plugin-updater = "2"
 
-# One UIKit property that wry does not set for us; stop_uikit_shrinking_the_viewport in lib.rs says
-# which one and why. These versions are the ones wry already resolves for its own iOS backend, so
-# matching them keeps a single copy of objc2 in the build rather than a second incompatible one.
+# Two things wry leaves to us: one UIKit property (stop_uikit_shrinking_the_viewport in lib.rs) and
+# the SFSafariViewController that shows the consent page (google/browser.rs). These versions are the
+# ones wry already resolves for its own iOS backend, so matching them keeps a single copy of objc2 in
+# the build rather than a second incompatible one.
 [target.'cfg(target_os = "ios")'.dependencies]
 objc2 = "0.6"
 objc2-ui-kit = { version = "0.3", default-features = false, features = [
@@ -55,6 +56,14 @@ objc2-ui-kit = { version = "0.3", default-features = false, features = [
   "UIView",
   "UIScrollView",
 ] }
+objc2-foundation = { version = "0.3", default-features = false, features = [
+  "std",
+  "NSString",
+  "NSURL",
+] }
+# Only for the null completion handler the two present/dismiss calls take. Passing a raw null
+# pointer there would encode as an object rather than a block, which objc2 checks and rejects.
+block2 = "0.6"
 
 [dev-dependencies]
 tempfile = "3"