Initial artdag-common shared library

Shared components for L1 and L2 servers:
- Jinja2 template system with base template and components
- Middleware for auth and content negotiation
- Pydantic models for requests/responses
- Utility functions for pagination, media, formatting
- Constants for Tailwind/HTMX/Cytoscape CDNs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,22 @@
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[project]
+name = "artdag-common"
+version = "0.1.0"
+description = "Shared components for Art-DAG L1 and L2 servers"
+requires-python = ">=3.10"
+dependencies = [
+    "fastapi>=0.100.0",
+    "jinja2>=3.1.0",
+    "pydantic>=2.0.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=7.0.0",
+]
+
+[tool.hatch.build.targets.wheel]
+packages = ["artdag_common"]