Restructure refimpl into go-lang and python subdirectories

Move Go reference implementation to refimpl/go-lang/ and add new
Python reference implementation in refimpl/python/. Update build.sh
with renamed draft and simplified tool paths.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

refimpl/python/ect/__init__.py

@@ -0,0 +1,61 @@
+# WIMSE Execution Context Tokens (ECT) — Python reference implementation
+# draft-nennemann-wimse-execution-context-00
+
+from ect.types import (
+    ECT_TYPE,
+    POL_DECISION_APPROVED,
+    POL_DECISION_REJECTED,
+    POL_DECISION_PENDING_HUMAN_REVIEW,
+    Payload,
+    valid_pol_decision,
+)
+from ect.create import create, generate_key, CreateOptions, default_create_options
+from ect.verify import (
+    ParsedECT,
+    parse,
+    verify,
+    VerifyOptions,
+    default_verify_options,
+    KeyResolver,
+)
+from ect.dag import (
+    ECTStore,
+    DAGConfig,
+    default_dag_config,
+    validate_dag,
+)
+from ect.ledger import Ledger, MemoryLedger, LedgerEntry, ErrTaskIDExists
+from ect.config import Config, default_config, load_config_from_env
+from ect.jti_cache import JTICache, new_jti_cache
+
+__all__ = [
+    "ECT_TYPE",
+    "POL_DECISION_APPROVED",
+    "POL_DECISION_REJECTED",
+    "POL_DECISION_PENDING_HUMAN_REVIEW",
+    "Payload",
+    "valid_pol_decision",
+    "create",
+    "generate_key",
+    "CreateOptions",
+    "default_create_options",
+    "ParsedECT",
+    "parse",
+    "verify",
+    "VerifyOptions",
+    "default_verify_options",
+    "KeyResolver",
+    "ECTStore",
+    "DAGConfig",
+    "default_dag_config",
+    "validate_dag",
+    "Ledger",
+    "MemoryLedger",
+    "LedgerEntry",
+    "ErrTaskIDExists",
+    "Config",
+    "default_config",
+    "load_config_from_env",
+    "JTICache",
+    "new_jti_cache",
+]