refactor(deploy): make TML import async-only (remove flag + sync branches)

Both table phases now call import_tmls_async directly — no TS_TML_IMPORT_MODE
flag, no sync path selection. The old sync closures (_import_tml_chunk,
_import_tmls_chunked, _resolve_/_verify_*_after_timeout) are now unreferenced
dead code; they'll be excised in a follow-up once one async build is validated
end-to-end (kept in git history as the fallback). Shared deploy_all → app + MCP.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

thoughtspot_deployer.py

@@ -2665,11 +2665,6 @@ class ThoughtSpotDeployer:
         
         _slog = session_logger
         _ts_error = None
-        # Async TML import (reliability fix for gateway 504s) — opt-in via env,
-        # default sync so behavior is unchanged until the flag is flipped.
-        use_async = os.getenv("TS_TML_IMPORT_MODE", "sync").strip().lower() == "async"
-        if use_async:
-            log_progress("   [async] TS_TML_IMPORT_MODE=async — async TML import enabled")
 
         try:
             import time
@@ -3410,20 +3405,11 @@ class ThoughtSpotDeployer:
                 f"   Sending table creation requests for {len(table_tmls_batch1)} tables "
                 f"(chunk size {create_chunk_size})..."
             )
-            if use_async:
-                objects = self.import_tmls_async(
-                    table_names_order, table_tmls_batch1, True,
-                    connection_guid, connection_name,
-                    log_progress=log_progress, slog=_slog,
-                )
-            else:
-                objects = _import_tmls_chunked(
-                    "Batch 1",
-                    table_names_order,
-                    table_tmls_batch1,
-                    create_new=True,
-                    chunk_size=create_chunk_size,
-                )
+            objects = self.import_tmls_async(
+                table_names_order, table_tmls_batch1, True,
+                connection_guid, connection_name,
+                log_progress=log_progress, slog=_slog,
+            )
 
             if objects is None:
                 return results
@@ -3532,21 +3518,11 @@ class ThoughtSpotDeployer:
                     f"   Sending join update requests for {len(table_tmls_batch2)} tables "
                     f"(chunk size {update_chunk_size})..."
                 )
-                if use_async:
-                    objects = self.import_tmls_async(
-                        table_names_order_batch2, table_tmls_batch2, False,
-                        connection_guid, connection_name,
-                        log_progress=log_progress, slog=_slog,
-                    )
-                else:
-                    objects = _import_tmls_chunked(
-                        "Batch 2",
-                        table_names_order_batch2,
-                        table_tmls_batch2,
-                        create_new=False,
-                        chunk_size=update_chunk_size,
-                        fatal_errors=False,
-                    )
+                objects = self.import_tmls_async(
+                    table_names_order_batch2, table_tmls_batch2, False,
+                    connection_guid, connection_name,
+                    log_progress=log_progress, slog=_slog,
+                )
 
                 if objects is not None:
                     # Process each result by table name. Partial retry recovery can