feat(nwsync): emit blobs and per-artifact NSYM, assemble merged manifests (#71)

Builds sow-tools#53. Format spec followed is the resolution comment of sow-platform#94, checked line by line against niv/neverwinter.nim at HEAD (`nwsync.nim`, `compressedbuf.nim`, `nwsync/private/libupdate.nim`).

## What lands

`crucible nwsync emit <artifact> --out DIR` — explodes one `.hak`/`.erf`, or one loose file such as the TLK, into NWSync blobs plus a NSYM v3 manifest covering only that artifact, with the same `.json` sidecar upstream writes. Blob path `data/sha1/<h0h1>/<h2h3>/<sha1>`, body in NWCompressedBuffer framing (magic `NSYC`, version 3, algorithm 2, uncompressed size, zstd header version 1, dictionary 0, raw zstd frame). The sha1 that names a blob is over the uncompressed bytes.

`crucible nwsync assemble --order NAMES --entries DIR --out DIR [--group-id N]` — merges the per-artifact manifests into one, reading no bulk data at all. Merge rule is resref shadowing, not concatenation: a resref in more than one artifact resolves to the earliest artifact in `--order`, which is how the game resolves it. `--group-id` stays caller-supplied (1 current, 2 testing; 0 is absent, matching upstream omitting a zero integer meta field).

Rules taken from upstream and not re-invented: `nss`/`ndb`/`gic` always skipped; an unresolvable restype is a hard error, not a skip; a resource over 15 MB fails closed; no `latest` file and no `.origin` file, ever. A `.mod` is refused outright — a persistent world publishes no module contents, so the module contributes no bytes.

## Two deliberate departures

- **Emitter version is its own field, not the build revision.** `emitter_version` is a constant bumped only when emitted bytes change. Keying the refuse-to-merge check on `created_with` would invalidate every published index on every unrelated crucible commit and force a re-emit of the whole 15 GB corpus — the opposite of "nothing downstream ever needs the hak again".
- **`SOURCE_DATE_EPOCH` pins the sidecar timestamp.** The manifest itself was already deterministic; the sidecar's `created` was not, against the determinism rule in `docs/consumer-contract.md`.

## Not in this PR, and why

- **Direct upload.** Only the local `--out` sink exists, which is the conformance path. The upload sink and the mid-hak-failure question are sow-tools#60, and the consumer wiring is #65.
- **The conformance run against upstream.** sow-tools#59 owns getting `nwn_nwsync_write` running and capturing reference output. The format here was read from upstream source rather than from its output, so the byte-for-byte manifest comparison and the after-decompression blob comparison still have to happen — that is what #59 is for. The tests in this PR check the layout against the spec, so a shared misreading would pass them.
- **The `artifacts/haks/sha256/<a>/<b>/<sha256>.nsym` location.** emit writes `<out>/<name>.nsym`; where a publisher puts it is the publisher's business (#65).
- **The acceptance gate** — a real client syncing from an assembled manifest — is unchanged and still open.

## Checks

`make check` green (vet, unit tests, shellcheck, yamllint, workflow contract), `make smoke` green with the new builder, `nix build .#crucible` produces `crucible-nwsync`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)Reviewed-on: #71

Co-authored-by: vickydotbat <vickydotbat@tutamail.com>

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)
 			}