Fix run item and batch mode robustness

- run item: rename tum_fime→tum, remove stdout=PIPE (deadlock with
  spawn), support batch mode (-b), SUCCESS on any completed subprocess
  regardless of sub-test result
- batch.py: fix control("loaded") deadlock via daemon thread + Event +
  is_alive() polling; fix premature finish on gd_update messages;
  propagate success flag from finished message; guard control("close")
- process.py: include success flag in send_finished message
- py_process/lua_process: add stdout/stderr=DEVNULL to Popen
- test_run.py: fix finished detection ("id" in m and m["id"] is None)
- testium_win.py: track run_exit_code, SIGABRT handler, clean exit
- __init__.py: sys.exit with batch success flag
- Add run item validation tests and CLAUDE.md documentation

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

test/validation/items/run/param.yaml

@@ -0,0 +1 @@
+no_param: Null

test/validation/items/run/sub_fail.tum

@@ -0,0 +1,7 @@
+main:
+    name: run sub-test (always fail)
+    steps:
+        - check:
+            name: fail
+            values:
+                - false

test/validation/items/run/sub_pass.tum

@@ -0,0 +1,7 @@
+main:
+    name: run sub-test (always pass)
+    steps:
+        - check:
+            name: pass
+            values:
+                - true

test/validation/items/run/test.tum

@@ -0,0 +1,25 @@
+# run item: launches a .tum file in a new testium instance.
+# In batch mode the sub-instance runs with -b; in GUI mode with -r.
+# The run item result is SUCCESS if the sub-instance launched successfully,
+# regardless of its own test result.
+
+- run:
+    name: run PASS (valid file, passing sub-test)
+    key: $(test)_PASS
+    tum: $(test_path)$(psep)sub_pass.tum
+
+- run:
+    name: run PASS (valid file, failing sub-test)
+    key: $(test)_PASS
+    tum: $(test_path)$(psep)sub_fail.tum
+
+- run:
+    name: run FAIL (file not found)
+    key: $(test)_FAIL
+    tum: $(test_path)$(psep)non_existent.tum
+
+- run:
+    name: run FAIL (wait_for_exec without time window)
+    key: $(test)_FAIL
+    tum: $(test_path)$(psep)sub_pass.tum
+    wait_for_exec: true