volume-manager: load the mount map; pick binary by signature, compose the id-path (S2)

The volume manager reads its policy from configuration at boot (loadTables,
mirroring the device-manager registry load): filesystems.csv (content signature
-> service binary) and volumes.csv (optional id -> mount-prefix override), each
held in a static source buffer with declared bounds. On probe it picks the
binary from the volume's signature (unserved + logged if no row matches, like an
unbound device) and composes the mount path — a volumes.csv override, else the
default /volumes/<id> from volume-map.idString — then spawns that binary with
argv {volume-id, mount-prefix}. Behavior-preserving: fat still ignores argv[2..]
and uses its hardcoded mounts, the binary resolves to /system/services/fat, so
the FULL suite stays green (127/127); the flip to argv-driven mounts and the
/volumes/usb -> id-path migration land in step 5.

system/services/volume-manager/build.zig

@@ -10,9 +10,10 @@ pub fn build(b: *std.Build) void {
         .name = "volume-manager",
         .root_source_file = b.path("volume-manager.zig"),
         .imports = &.{
-            "block",   "channel",  "device-manager-protocol", "driver",
-            "envelope", "ipc",     "logging",                 "memory",
-            "process", "service",  "time",                    "volume-manager-protocol",
+            "block",   "channel",     "csv",           "device-manager-protocol",
+            "driver",  "envelope",    "file-system",   "ipc",
+            "logging", "memory",      "process",       "service",
+            "time",    "volume-manager-protocol",
         },
     });
     b.installArtifact(exe);