Build optimization: pre-built PM3 binaries, ARM64 CI, base image caching

Replace PM3 compile-from-source in pi-gen with pre-built tarball extraction
(saves 43-58 min). Merge stagePM3 into stageDangerousPi as 02-pm3-install
substage, renumber all subsequent substages. Switch CI PM3 build to native
ARM64 runner (ubuntu-24.04-arm64) eliminating QEMU overhead. Add weekly
base-image workflow for pre-baking stages 0-2. Support PM3_TARBALL,
BASE_IMAGE, and APT_PROXY env vars in build-image.sh.

Also includes prior Phase 5 work: theme system, design system integration,
component update system, OS updates, CI build pipeline, and test results.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/backend/managers/ble_manager.py

@@ -210,7 +210,7 @@ class BLEManager:
         }
 
     async def _check_bluetooth_adapter(self) -> bool:
-        """Check if Bluetooth adapter is available.
+        """Check if Bluetooth adapter is available, unblocking and powering on if needed.
 
         Returns:
             True if adapter is available, False otherwise
@@ -224,8 +224,20 @@ class BLEManager:
             )
             stdout, stderr = await process.communicate()
 
-            # If we get output with "Controller", we have an adapter
-            return b"Controller" in stdout
+            if b"Controller" not in stdout:
+                return False
+
+            # Unblock Bluetooth if soft-blocked by rfkill
+            await self._run_cmd("rfkill", "unblock", "bluetooth")
+
+            # Power on the adapter via bluetoothctl
+            out = await self._run_cmd("bluetoothctl", "power", "on")
+            if b"succeeded" in out.lower() or b"yes" in out.lower():
+                logger.info("Bluetooth adapter powered on")
+            else:
+                logger.warning("Bluetooth power on response: %s", out.decode(errors='replace').strip())
+
+            return True
 
         except FileNotFoundError:
             logger.warning("bluetoothctl not found - BlueZ not installed")
@@ -234,6 +246,19 @@ class BLEManager:
             logger.error("Error checking Bluetooth adapter: %s", e)
             return False
 
+    async def _run_cmd(self, *args: str) -> bytes:
+        """Run a command and return stdout."""
+        try:
+            process = await asyncio.create_subprocess_exec(
+                *args,
+                stdout=asyncio.subprocess.PIPE,
+                stderr=asyncio.subprocess.PIPE
+            )
+            stdout, _ = await process.communicate()
+            return stdout
+        except FileNotFoundError:
+            return b""
+
     async def _set_device_name(self, name: str):
         """Set the Bluetooth device name.