android: Share → ThoughtSync, and a "New note" entry in the selection toolbar

Capture without opening the app first — the input half of #1899. Two ways in:
the share sheet from anywhere, and the text-selection toolbar in any app's
text field.

## The note is created, not pre-filled

The obvious build is "open the editor on a draft holding the shared text".
That silently loses it. `NoteEditorScreen`'s flush is guarded by
`bodyText != note.body`, so a draft handed the text already has nothing to
save — share a link, press back without typing, and it is gone. Which is
exactly the shape of a share: the common case is walking away.

So `captureShared` makes the row first and opens the editor on the real
note. A share has already said "keep this"; creating it is what honours
that, and back then leaves a saved note rather than a decision.

## launchMode="singleTop"

The reminder notification adds FLAG_ACTIVITY_SINGLE_TOP to its own intent,
which is why `onNewIntent` already worked there. A share intent is built by
the OTHER app and nothing here can add a flag to it, so the activity has to
declare it. Without that, every share while the app was running would stack a
second MainActivity — a second view model, a second board, and a back press
landing on a stale copy of the same app.

## Subject and text, both

A browser sends EXTRA_SUBJECT as the page title and EXTRA_TEXT as the URL.
Keeping both makes the note read as its title, because the core names a note
by its first line — the difference between a board you can scan and a column
of identical links. `distinct` because plenty of senders put the same string
in both.

The extras are removed on read, like the reminder's note id and for the same
reason: the activity keeps its launch intent, so without consuming them a
rotation would replay the share and mint the note again.

## Not included: images

`image/*` is deliberately absent from the filter. Nothing in this app can
create an attachment — the core has `delete_attachment` and no counterpart,
and the FFI exposes neither. Declaring the mime type would put ThoughtSync in
front of people in the share sheet for a job it cannot do, and fail after
they had already chosen it. Adding it needs an attachment-creation path
through the core, the FFI and sync, which is its own piece of work.

The desktop half of #1899 — a global hotkey — is not in this commit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K3MMqUtzX1TJgA1oypvm1c

android/app/src/main/AndroidManifest.xml

@@ -99,15 +99,53 @@
         android:supportsRtl="true"
         android:theme="@style/Theme.ThoughtSync"
         android:usesCleartextTraffic="true">
+        <!--
+          launchMode="singleTop" exists for the SHARE filters below.
+
+          The reminder notification adds FLAG_ACTIVITY_SINGLE_TOP to its own
+          intent, so onNewIntent already worked for that one. A share intent is
+          built by the OTHER app — Chrome, a reader, the text-selection toolbar —
+          and nothing here can add a flag to it. Without singleTop declared on the
+          activity itself, every share while the app is running would stack a
+          second MainActivity on top of the first: a second view model, a second
+          board, and a back press that lands on a stale copy of the same app.
+        -->
         <activity
             android:name=".MainActivity"
             android:exported="true"
+            android:launchMode="singleTop"
             android:windowSoftInputMode="adjustResize"
             android:theme="@style/Theme.ThoughtSync">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
+
+            <!--
+              Capture without opening the app first: Share → ThoughtSync from
+              anywhere, and the selection toolbar in any text field.
+
+              text/plain ONLY, and image/* deliberately absent. Nothing in this
+              app can create an attachment — the core has `delete_attachment` and
+              no counterpart, and the FFI exposes neither. Claiming images in the
+              share sheet would put this app in front of people for a job it
+              cannot do and fail after they had chosen it.
+            -->
+            <intent-filter>
+                <action android:name="android.intent.action.SEND" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <data android:mimeType="text/plain" />
+            </intent-filter>
+
+            <!--
+              The label is what appears in the text-selection menu beside Copy and
+              Share, where "ThoughtSync" would say who rather than what.
+            -->
+            <intent-filter android:label="@string/capture_process_text">
+                <action android:name="android.intent.action.PROCESS_TEXT" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <data android:mimeType="text/plain" />
+            </intent-filter>
         </activity>
 
         <!--