Split experiments from tests

The tests/ directory held 50 laboratory programs and no tests. They model
channels, run hundreds of repetitions and write CSV, PNG and reports;
calling that a test suite blocked introducing a real one, because any
pytest run would have collected the labs and re-executed every
experiment.

- move all 50 lab programs to experiments/ with git mv, preserving history
- rewrite the 38 cross-imports between labs from tests.labNNN to
  experiments.labNNN
- leave tests/ empty for actual fast checks of protocol/
- point quick_gate and the hook at the new layout and add experiments/ to
  the syntax sweep
- update the paths quoted in the Lab042 specification and the verifier
  agent definition

This also defuses the import-time work finding without touching 41 files:
the labs still create directories and write files on import, but nothing
imports them now except the gate, which does so deliberately.

Gate passes: syntax clean, protocol imports, 15 lab modules import, 2
functional suites run.

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

tools/quick_gate.py

@@ -24,7 +24,7 @@ import sys
 import traceback
 
 PROJECT_ROOT = Path(__file__).resolve().parent.parent
-CHECKED_DIRECTORIES = ("protocol", "tests", "tools")
+CHECKED_DIRECTORIES = ("protocol", "tests", "experiments", "tools")
 
 
 def check_syntax() -> list[str]:
@@ -81,13 +81,13 @@ def check_functional_tests() -> tuple[list[str], int, int]:
     executed = 0
     skipped = 0
 
-    for path in sorted((PROJECT_ROOT / "tests").glob("lab*.py")):
+    for path in sorted((PROJECT_ROOT / "experiments").glob("lab*.py")):
         source = path.read_text(encoding="utf-8")
 
         if "def run_functional_tests" not in source:
             continue
 
-        module_name = f"tests.{path.stem}"
+        module_name = f"experiments.{path.stem}"
 
         try:
             module = importlib.import_module(module_name)