Re-architect Sentinel as a zero-dependency Python package

Port the bash prototype to a structured, testable Python codebase while
preserving the same control loop and the seven detection signatures. The bash
implementation stays in src/ as the regression oracle.

Highlights:
- enodia_sentinel/ package (stdlib only — no runtime deps):
  - detectors/ : one pure function per signature, detect(state, cfg)->Alerts
  - system.py  : SystemState — one cached /proc + ss snapshot per sweep,
                 fully injectable so detectors are unit-testable
  - daemon.py  : sweep loop, in-process cooldown dedup, threaded snapshot
                 capture, and a SUID filesystem scan moved OFF the loop
                 thread onto a slow background cadence
  - snapshot.py: forensic text + JSON sidecar with per-signature IR guidance
  - config.py  : dataclass config via TOML + env overrides
  - netutil.py : public-IP / CIDR logic via stdlib ipaddress
- tests/ : 25 stdlib-unittest cases (no root, no /proc, no ss needed)
- TOML config, launcher wrapper, Makefile (pip-free install), hardened
  systemd unit (env-resolved ExecStart), updated PKGBUILD, rewritten README

Performance: per-sweep cost ~200 ms (shared cached state); the multi-second
SUID walk no longer blocks detection. scandir-based walk replaces os.walk.

Verified on Arch: all 7 detectors fire on red-team drills (reverse_shell,
ld_preload, deleted_exe, new_listener, new_suid confirmed live end-to-end),
no false positives on a clean sweep, 25/25 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,25 @@
+[build-system]
+requires = ["setuptools>=61"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "enodia-sentinel"
+version = "0.2.0"
+description = "Host intrusion-detection daemon — signature-based detection of reverse shells, LD_PRELOAD rootkits, fileless malware, and persistence tampering"
+readme = "README.md"
+requires-python = ">=3.11"
+license = { text = "MIT" }
+authors = [{ name = "Enodia" }]
+keywords = ["security", "ids", "hids", "detection", "linux", "forensics"]
+# Zero runtime dependencies — stdlib only, by design (a system security
+# daemon should not pull in a dependency tree it has to trust and update).
+dependencies = []
+
+[project.scripts]
+enodia-sentinel = "enodia_sentinel.cli:main"
+
+[project.optional-dependencies]
+dev = ["pytest"]
+
+[tool.setuptools.packages.find]
+include = ["enodia_sentinel*"]