feat(nwsync): emit blobs and per-artifact NSYM, assemble merged manifests

Adds `crucible nwsync emit` and `crucible nwsync assemble`, the split
replacement for upstream nwn_nwsync_write, which cannot be used because it
wants every hak, the TLK and the module present in one run on one disk.

emit explodes one artifact — a .hak/.erf or a loose file such as the TLK —
into NWSync blobs (NWCompressedBuffer framing, magic NSYC, zstd) plus a NSYM
v3 manifest describing only that artifact, with the same .json sidecar
upstream writes. Blob names are the sha1 of the uncompressed bytes, restypes
nss/ndb/gic are always skipped, an unresolvable restype is a hard error, a
resource over 15 MB fails closed, and no latest or .origin file is ever
written.

assemble merges the per-artifact manifests into one, reading no bulk data.
The merge rule is resref shadowing, not concatenation: a resref present in
more than one artifact resolves to the earliest artifact in --order, the way
the game resolves it. It refuses to merge across mismatched emitter versions,
and takes --group-id from the caller (1 current, 2 testing; 0 is absent).

Refs #53.

internal/dispatch/dispatch_test.go

@@ -148,6 +148,10 @@ func TestBuilderHelpIsOK(t *testing.T) {
 	}
 }
 
+// selfContained builders parse their own subcommands instead of delegating to
+// the legacy internal/app surface.
+var selfContained = map[string]bool{"depot": true, "assets": true, "nwsync": true}
+
 func TestCanonicalCommandSurface(t *testing.T) {
 	want := map[string][]string{
 		"depot":   {"status", "push", "verify", "get", "pull"},
@@ -156,6 +160,7 @@ func TestCanonicalCommandSurface(t *testing.T) {
 		"module":  {"build", "extract", "validate", "compare", "manifest"},
 		"topdata": {"validate", "build", "package", "compare", "convert"},
 		"wiki":    {"build", "deploy"},
+		"nwsync":  {"emit", "assemble"},
 	}
 	for _, builder := range Registry {
 		got := builder.subcommands()
@@ -173,10 +178,10 @@ func TestRegistryCommandNamesAndAliasesAreUnambiguous(t *testing.T) {
 	for _, builder := range Registry {
 		seen := map[string]bool{}
 		for _, command := range builder.Commands {
-			// depot and assets parse their own subcommands and bypass AppCommand
-			// routing entirely (see the self-contained-builder branch in
-			// runBuilder), so their Commands carry no AppCommand.
-			requireAppCommand := builder.Name != "depot" && builder.Name != "assets"
+			// depot, assets and nwsync parse their own subcommands and bypass
+			// AppCommand routing entirely (see the self-contained-builder branch
+			// in runBuilder), so their Commands carry no AppCommand.
+			requireAppCommand := !selfContained[builder.Name]
 			if command.Name == "" || command.Summary == "" || command.Usage == "" || (requireAppCommand && command.AppCommand == "") {
 				t.Errorf("%s has incomplete command metadata: %#v", builder.Name, command)
 			}