Stabilize first-run cudagraph timing and colorize terminal output

- _cudagraph_plugin: warm up autotune/JIT explicitly before graph capture
  (internal 5-iter warmup is too short), tag fallback markers with the
  failing phase; first-run latency no longer jitters run-to-run.
- _device_guard_plugin (new): set GEMS_VENDOR via torch probe before
  importing flag_gems, avoiding its timeout-less nvidia-smi subprocess
  probe that can hang import in fork-broken environments.
- _pretty_report_plugin (new) + _term_style (new): fold inputs identical
  across all result rows into a legend line, color status/plugin
  tags/markers on the live terminal; run.log is ANSI-stripped and keeps
  upstream SUCCESS/column wording for grep compatibility.
- run_pytest.sh: make USE_FLAGTUNE overridable, group all knobs into a
  config section with Chinese comments, add start/end banners.
- README: document the warmup semantics, new plugins/env vars, and the
  A/B rule that both sides must use the same USE_FLAGTUNE.

_autotune_record_plugin.py

@@ -115,8 +115,10 @@ def _compute_key(tuner: Any, args: Tuple[Any, ...], kwargs: Dict[str, Any]) -> O
 
 def _emit_marker(reason: str) -> None:
     # Marker lands in run.log (grep it to audit replay coverage); flush so it
-    # appears before the kernel runs.
-    print(f"AUTOTUNE_REPLAY_FALLBACK reason={reason}", flush=True)
+    # appears before the kernel runs. Yellow on the live terminal only —
+    # run_pytest.sh strips ANSI from run.log.
+    from _term_style import YELLOW, paint
+    print(paint(f"AUTOTUNE_REPLAY_FALLBACK reason={reason}", YELLOW), flush=True)
 
 
 def _record_run(original):
@@ -235,16 +237,19 @@ def _dump_record(record_dir: str) -> None:
         path.write_text(json.dumps(payload, indent=2, ensure_ascii=False) + "\n")
     except Exception as exc:
         # Don't break the run if dump fails; the perf row is still produced.
-        print(f"[autotune-record-plugin] dump failed: {exc}", file=sys.stderr, flush=True)
+        from _term_style import tag
+        print(f"{tag('[autotune-record-plugin]')} dump failed: {exc}",
+              file=sys.stderr, flush=True)
 
 
 def pytest_configure(config):
+    from _term_style import tag
     record_dir = os.environ.get(_RECORD_DIR_ENV, "").strip()
     replay_dir = os.environ.get(_REPLAY_DIR_ENV, "").strip()
     if record_dir and replay_dir:
         # Mutually exclusive: recording while replaying is pointless. Surface loudly.
-        print("[autotune-record-plugin] error: both RECORD_DIR and REPLAY_DIR set; "
-              "ignoring both (no-op)", file=sys.stderr, flush=True)
+        print(f"{tag('[autotune-record-plugin]')} error: both RECORD_DIR and "
+              "REPLAY_DIR set; ignoring both (no-op)", file=sys.stderr, flush=True)
         return
     if not record_dir and not replay_dir:
         return
@@ -265,11 +270,11 @@ def pytest_configure(config):
         # atexit (not sessionfinish): persist whatever was recorded even if an op
         # crash kills the session; a later replay run falls back for missing keys.
         atexit.register(_dump_record, record_dir)
-        print(f"[autotune-record-plugin] recording autotune configs to "
+        print(f"{tag('[autotune-record-plugin]')} recording autotune configs to "
               f"{_record_path(record_dir)} ({'+'.join(patched)})",
               file=sys.stderr, flush=True)
     else:
         loaded = _load_replay_dir(replay_dir)
-        print(f"[autotune-record-plugin] replaying {loaded} recorded entries from "
+        print(f"{tag('[autotune-record-plugin]')} replaying {loaded} recorded entries from "
               f"{_record_path(replay_dir)} ({'+'.join(patched)})",
               file=sys.stderr, flush=True)