Add FAT12/16/32 scheme daemon, management tools, and build integration

5-crate Rust workspace implementing full VFAT support: fatd scheme daemon
(FSScheme with open/read/write/mkdir/unlink/rename/fstat), fat-mkfs (create
FAT12/16/32 with labels and cluster size), fat-label (read/write BPB + root-dir
volume labels), fat-check (verify + repair dirty flags, FSInfo, lost clusters,
orphaned LFN). 60 unit tests, 0 unwrap in production code. Included in all 5
redbear configs via redbear-device-services.toml.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

config/redbear-device-services.toml

@@ -1,9 +1,10 @@
 # Red Bear OS shared device-service wiring
 #
-# Shared by profiles that ship the firmware/input/Wi-Fi control compatibility stack.
+# Shared by profiles that ship the firmware/input/Wi-Fi/FAT control compatibility stack.
 
 [packages]
 redbear-quirks = {}
+fatd = {}
 
 [[files]]
 path = "/lib/firmware"
@@ -67,3 +68,18 @@ requires_weak = [
 cmd = "evdevd"
 type = "oneshot_async"
 """
+
+[[files]]
+path = "/usr/lib/init.d/15_fatd.service"
+data = """
+[unit]
+description = "FAT filesystem scheme daemon"
+requires_weak = [
+    "00_pcid-spawner.service",
+]
+
+[service]
+cmd = "fatd"
+args = ["disk/live-virtio", "fat-live"]
+type = { scheme = "fat-live" }
+"""