Add event-taxonomy package with canonical schema, adapters, and CLI

Canonical NormalizedFinding schema with Severity enum (CRITICAL/HIGH/MEDIUM/LOW/INFO).
Per-project adapters for 9 tools with severity mapping for string labels, int 1-10,
float 0-1, Python Enum, and computed properties. CLI pipe interface and registry.

Nightshift-Task: event-taxonomy
Nightshift-Ref: https://github.com/marcus/nightshift

pyproject.toml

@@ -0,0 +1,19 @@
+[project]
+name = "event-taxonomy"
+version = "0.1.0"
+description = "Normalize event naming and structure across analysis tools"
+requires-python = ">=3.13"
+dependencies = []
+
+[project.scripts]
+event-taxonomy = "event_taxonomy.__main__:main"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["src/event_taxonomy"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]