feat: v0.6.0 — demo parity & production hardening

[23min]

Summary

• Complete Builder helpers — all 18 standard component types now have Builder helpers (was 11): date_time_input, choice_picker, icon, video, audio_player, list, tabs
• Complete debug renderer — all 18 types render in priv/static/index.html (was 7): TextField, Slider, DateTimeInput, ChoicePicker, Image, Icon, Video, AudioPlayer, List, Tabs, Modal
• Telemetry instrumentation — [:a2ui, :socket, :init|:action|:terminate] and [:a2ui, :sse, :init|:event] events (uses existing transitive dep, no new dependency)
• Graceful error handling — provider crashes in handle_action/2, handle_info/2, handle_error/2 are caught via try/rescue and logged instead of crashing the socket
• 5 demo providers in demo/ — Component Gallery, Data Binding, Form Validation, Push Streaming, Custom Component
• Query param routing — ?demo=gallery|binding|form|push|custom selects demo provider; debug renderer forwards params to WS URL
• Docs updated — README, ROADMAP, CHANGELOG, CLAUDE.md all reflect v0.6.0 with current module map and test count

232 tests, 0 failures.

Test plan

• mix ci passes (format + compile warnings-as-errors + 232 tests)
• mix docs generates without warnings
• mix run demo_server.exs — open http://localhost:4000, verify all 18 component types render in gallery demo
• Switch demos via ?demo=binding, ?demo=form, ?demo=push, ?demo=custom
• Verify push streaming demo updates live metrics every second

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