fix: address code review findings — batch args, venv path, serve flags

- Fix missing BATCH_ARGS in long-context commands (both benchmark scripts)
- Fix CLAUDE.md stale venv path (data/venv → .venv) and add serve/power docs
- Add -b/--batch to bin/benchmark help text
- Add --no-think flag to serve script (--reasoning-budget 0)
- Sanitize model names in eval run directories
- Simplify agentic setup to use requirements.txt
- Add serve --help test, batch flag assertions to existing tests
- Add requirements.txt for reproducible venv setup (Python 3.13)

tests/benchmark_flags.bats

@@ -11,6 +11,7 @@ load test_helper.sh
     assert_output --partial "--category"
     assert_output --partial "--skip-longctx"
     assert_output --partial "--kv-types"
+    assert_output --partial "--batch"
 }
 
 @test "run-suite --help shows usage and exits 0" {
@@ -22,6 +23,7 @@ load test_helper.sh
     assert_output --partial "--skip-longctx"
     assert_output --partial "--tag"
     assert_output --partial "--kv-types"
+    assert_output --partial "--batch"
 }
 
 @test "benchmark dispatcher shows help with no args" {
@@ -31,6 +33,18 @@ load test_helper.sh
     assert_output --partial "--max-size"
     assert_output --partial "--skip-longctx"
     assert_output --partial "--kv-types"
+    assert_output --partial "--batch"
+}
+
+@test "serve --help shows usage and exits 0" {
+    run bash "$PROJECT_ROOT/bin/serve" --help
+    assert_success
+    assert_output --partial "Usage"
+    assert_output --partial "--model"
+    assert_output --partial "--ngram"
+    assert_output --partial "--no-think"
+    assert_output --partial "--ctx"
+    assert_output --partial "--port"
 }
 
 @test "benchmark dispatcher passes --help through to baseline" {