feat(android): open share links from a browser or the share sheet

A drive.proton.me/urls/ link opened from a browser, or text containing
one shared to the app, switches to Shares and opens the Add form with
the link filled in, fragment included. A playing episode moves to the
mini transport instead of covering the form. A recreated activity does
not offer the same link again.

The view filter is not autoVerify, since the domain is Proton's, so
Android only routes browser links here once "Open supported links" is
allowed in the app's settings; sharing works without that.

android/app/src/main/java/io/narl/protonstream/MainActivity.kt

@@ -48,6 +48,9 @@ import uniffi.pstr_android.PaletteRecord
 class MainActivity : ComponentActivity() {
     private val playerHost = mutableStateOf<NativeMpvHost?>(null)
     private val inPictureInPicture = mutableStateOf(false)
+
+    /** A share link handed over by a browser or the share sheet, until the Add form takes it. */
+    private val incomingShareLink = mutableStateOf<String?>(null)
     /**
      * Whether a bind is outstanding, which is what has to be unbound.
      *
@@ -97,6 +100,9 @@ class MainActivity : ComponentActivity() {
         // Infallible by construction — an unreadable theme file resolves to the
         // shipped default rather than throwing.
         runCatching { NativeRuntime.storedPalette() }.onSuccess(AppearanceState::seed)
+        // Only on a fresh start: a recreated activity is handed the intent it
+        // was launched with again, and would offer to add the same share twice.
+        if (savedInstanceState == null) incomingShareLink.value = intent.shareLink()
         enableEdgeToEdge()
         // Re-applied on every change, not just at startup: picking Latte from
         // the settings page has to turn the status bar's icons dark in the same
@@ -134,7 +140,12 @@ class MainActivity : ComponentActivity() {
         }
         setContent {
             ProtonStreamTheme {
-                ProtonStreamApp(playerHost.value, inPictureInPicture.value)
+                ProtonStreamApp(
+                    playerHost.value,
+                    inPictureInPicture.value,
+                    shareLink = incomingShareLink.value,
+                    onShareLinkTaken = { incomingShareLink.value = null },
+                )
             }
         }
     }
@@ -159,6 +170,13 @@ class MainActivity : ComponentActivity() {
         }
     }
 
+    // singleTask: a link opened while the app is running arrives here, not in
+    // a second activity.
+    override fun onNewIntent(intent: Intent) {
+        super.onNewIntent(intent)
+        intent.shareLink()?.let { incomingShareLink.value = it }
+    }
+
     override fun onUserLeaveHint() {
         super.onUserLeaveHint()
         // The backstop for launchers that still send this instead of arming