sdk(D.1 step 3 + release): module rename to go.attesto.eu/sdk + 0.3.0 bump

go.mod becomes module go.attesto.eu/sdk; all internal imports (CLI,
connectorkit, examples), the publication-evidence/registry contracts, docs,
and the README install line follow. No rotz.ai hostname remains in the
customer-visible Go chain. All Go packages build and pass under the new path.

All three SDKs bump to 0.3.0 (Python version.py/pyproject, TS package.json +
SDK_VERSION, Go SDKVersion + cliVersion) — the Phase-1 release version,
shipped atomically with the registry publish so the publication-evidence
contract stays consistent. Full sweep green: Python 84, TS 55, Go 3 packages.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

examples/proofstream/main.go

@@ -6,7 +6,7 @@ import (
 	"log"
 	"os"
 
-	attesto "git.rotz.ai/rotzmediagroup/attesto-v1/sdk/go"
+	attesto "go.attesto.eu/sdk"
 )
 
 func main() {