feat: add web UI dashboard with upload, review, and HTML export (#33)

Flask-based web dashboard with drag-and-drop upload, session management,
design summary view, component/net tables, and HTML report download.
Self-contained dark theme with no external dependencies. 10 tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: RFingAdam

src/mcp_pcb_emcopilot/web/__init__.py

@@ -0,0 +1 @@
+"""Web UI dashboard for PCB design review."""