Update shared Gaia workflows and Sargo development tooling

Fix camera switching and Contacts/SMS activity routing across shared hosts.
Integrate Marketplace installation and native standalone recovery tools,
Bluetooth runtime packages and trusted certificates.

Update English/French READMEs and the shared changelog with tested scope
and remaining radio/audio/Bluetooth limitations. Preview17 remains the
existing APK; no new native image is released.

Validation: shared JavaScript and native Python tests; Android packaging
and payload parity from an isolated publication checkout.

tundra/tools/sparse_backup.py

@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: MPL-2.0
+"""Decode the read-only TUNRAW1 stream; reject truncation and overlapping blocks."""
+import struct
+
+
+def exact(stream, length):
+    data=bytearray()
+    while len(data)<length:
+        block=stream.read(length-len(data))
+        if not block:raise ValueError('Truncated backup stream')
+        data.extend(block)
+    return bytes(data)
+
+
+def receive(stream, target, expected_size):
+    if exact(stream,8)!=b'TUNRAW1\0':raise ValueError('Unexpected backup protocol')
+    end=0
+    while True:
+        offset,length=struct.unpack('<QQ',exact(stream,16))
+        if not length:
+            if offset!=expected_size or stream.read(1):raise ValueError('Backup size or trailer mismatch')
+            target.truncate(expected_size)
+            return
+        if offset<end or length>65536 or offset+length>expected_size:raise ValueError('Invalid backup extent')
+        target.seek(offset);target.write(exact(stream,length));end=offset+length