Add real-time web dashboard

[ojongerius]

Summary

• Adds embedded web dashboard at :8080 — single HTML file, no build step, no external dependencies
• Live tool call stream via Server-Sent Events (SSE) for real-time monitoring
• Session sidebar with server name, tool call counts, and risk indicators
• Tool call table with filters by policy action (flag/pause/block) and operation type (read/write/delete/execute)
• Intent chain visualization showing temporal groupings of related tool calls
• One-click hash chain verification from the browser
• Approve/deny paused tool calls directly from the dashboard
• Dashboard stats bar: sessions, active, tool calls, flagged, blocked, avg risk
• Replaces the 3 inline HTTP handlers in main.go with the full internal/web package

Architecture

• internal/web/server.go — HTTP handlers, SSE hub, go:embed static files
• internal/web/static/index.html — dark-themed single-page dashboard (vanilla JS, no framework)
• internal/audit/queries.go — query methods for ListSessions, ListToolCalls, ListIntents, GetStats
• internal/proxy/proxy.go — broadcasts tool call events to SSE clients via Dashboard.Broadcast()

Test plan

• make build succeeds
• make test — all existing + new tests pass
• make lint clean
• Manual: start proxy, open http://localhost:8080, verify dashboard loads
• Manual: trigger tool calls, verify they appear in real-time
• Manual: verify intent chains tab shows temporal groupings
• Manual: verify hash chain verification works from browser