docs: reposition from 'firewall' to intent-bound action authorization

[koishore]

Aligns the repo's product positioning with the rest of delego (landing, spec, LinkedIn): "intent-bound action authorization for AI agents", replacing the older "policy & audit firewall" framing.

Prose changed (8 files)

• README.md headline, ARCHITECTURE.md, SECURITY.md, CONTRIBUTING.md, ROADMAP.md intros
• pyproject.toml description (flows to PyPI)
• delego/__init__.py module docstring tagline
• delego/audit.py docstring ("the firewall makes" → "delego makes")

Intentionally NOT changed

• The Firewall class and build_firewall() public API, their exports, and all firewall/make_firewall test fixtures and test_firewall_* names — renaming these is a breaking API change, out of scope for a positioning fix.
• Code/object references to the Firewall instance in docstrings (engine/cli/mcp_server/etc.), README "MCP gateways/firewalls" (other tools), CHANGELOG history, and examples/demo.py object references.

Verification

• python -m py_compile delego/*.py ✓
• import delego; from delego import Firewall, build_firewall ✓
• examples/demo.py runs end-to-end (allow / deny / approval / tamper-detection) ✓ — prose-only, no behavior change.

🤖 Generated with Claude Code