feat(detection): language-scoped rules + multi-language benchmark corpora

Rebuild the quick-scan detection engine and ground-truth benchmarks to hit
>=90% recall / <10% false positives for C/C++, Python, JavaScript, and Java.

Engine (findings.py, preprocess.py):
- Scope each PatternRule by language (fixes cross-language false positives such
  as the Python eval/exec rule firing on JS .exec()).
- Add JavaScript/TypeScript rules (command exec, eval/Function, reflected XSS,
  SQLi, path traversal, SSRF, weak hash, deserialization); execFile/spawn-argv
  excluded as safe alternatives.
- Add Java rules (Runtime exec, SQL string concatenation, weak hash, readObject)
  and a Groovy server-side template rule (yieldUnescaped of a bound variable).
- Broaden C/C++ and Python coverage; precision guards for format strings and
  parameterised vs concatenated SQL; #-comment skipping; CWE in rationale.
- Register .java/.groovy/.tpl source extensions.

Benchmarks:
- Add realistic corpora modeled on Damn Vulnerable C/C++, PyGoat/DVPWA, and
  NodeGoat, plus the real kiview/damn-vulnerable-spring-boot-app vendored
  verbatim (MIT, attribution in LICENSE/NOTICE.md). Each manifest carries
  complete, independently-labeled ground truth including genuinely
  hard-to-detect vulns (integer overflow, second-order SQLi, prototype
  pollution) so recall is measured honestly, plus safe-API files for precision.
- Fix pre-existing smoke-manifest ground-truth errors (Python/JS line offsets,
  missing C/C++ strcpy entry, Java SQLi line).

benchmark.py:
- Fix sink matching to normalise the expected sink consistently so sinks with
  underscores (e.g. render_template_string) can match.

Tests:
- Add tests/test_detection_benchmarks.py enforcing the >=90% recall / <10% FP
  goal per language and overall.

Measured: C/C++ 93.3%, Python 93.3%, JavaScript 92.3%, Java 100%;
overall 93.6% recall, 0.0% false-positive rate.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

benchmarks/fixtures/python-vulnerable/safe.py

@@ -0,0 +1,30 @@
+"""Safe equivalents. None of these lines should produce a finding."""
+import hashlib
+import subprocess
+
+import yaml
+from flask import request
+
+
+def ping_safe(host):
+    # list-form subprocess without shell is not command injection
+    return subprocess.check_output(["ping", "-c", "1", host])
+
+
+def user_safe(db):
+    name = request.args["name"]
+    # parameterised query: %s here is a bound placeholder, not %-formatting
+    return db.execute("select * from users where name = %s", (name,))
+
+
+def config_safe(data):
+    return yaml.safe_load(data)  # safe_load is not the unsafe yaml.load sink
+
+
+def token_safe(pw):
+    return hashlib.sha256(pw.encode()).hexdigest()  # strong hash
+
+
+def comment_only():
+    # os.system("rm -rf /") would be dangerous but this is a comment
+    return "ok"