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/boot/sparse-backup.c

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: MPL-2.0
+ * Read stdin only. Emit offsets and nonzero 64 KiB blocks for a host-side backup.
+ * No device is opened or written by this process.
+ */
+#define _start unused_stage0_start
+#include "init.c"
+#undef _start
+static unsigned long buffer[8192];
+static void stop(long code) {
+  call(NR_exit, code, 0, 0, 0, 0);
+  for (;;) {}
+}
+static void write_all(const void *data, long length) {
+  const char *p = data;
+  while (length) {
+    long n = call(NR_write, 1, (long)p, length, 0, 0);
+    if (n == -4) continue;
+    if (n <= 0) stop(3);
+    p += n;
+    length -= n;
+  }
+}
+__attribute__((noreturn)) void _start(void) {
+  unsigned long offset = 0;
+  write_all("TUNRAW1\0", 8);
+  for (;;) {
+    long n = call(NR_read, 0, (long)buffer, sizeof(buffer), 0, 0);
+    if (n == -4) continue;
+    if (n < 0) stop(2);
+    if (!n) break;
+    unsigned long bits = 0;
+    long i = 0;
+    for (; i + 8 <= n; i += 8) bits |= buffer[i / 8];
+    for (; i < n; ++i) bits |= ((unsigned char *)buffer)[i];
+    if (bits) {
+      unsigned long header[2] = {offset, (unsigned long)n};
+      write_all(header, sizeof(header));
+      write_all(buffer, n);
+    }
+    offset += n;
+  }
+  unsigned long end[2] = {offset, 0};
+  write_all(end, sizeof(end));
+  call(NR_exit, 0, 0, 0, 0, 0);
+  for (;;) {}
+}