Add cmd/inspect: eventbus + LiveView demo

[kaeawc]

Summary

• New `cmd/inspect` binary wires `internal/eventbus` into `tui.LiveView`. The `Inspector` subscribes to an `eventbus.Async[Event]`, accumulates counters + a ring buffer of the most recent events, exposes itself as a `tui.LiveSampler`.
• Three synthetic scenarios drive the bus: `steady` (10/s, info-only), `bursty` (50-event bursts every 2s), `noisy` (20/s mixed levels).
• Picker → LiveView dashboard → Done. Global quit shuts down the producer + inspector + bus before `tea.Quit`.
• Renderer is split into `renderHeader`/`renderLevelTable`/`renderKindTable`/`renderRecent` to keep the top-level fn under gocyclo.
• Headless: `--scenario X --duration Y --yes` for CI / demo runs.

Test plan

• Inspector accumulates totals, ring-buffers to capacity, returns copied maps from Snapshot
• Stop() freezes Elapsed; Sample reports done after Stop
• Scenario lookup matrix
• runSteady + runNoisy actually publish events in a bounded window (race-safe poll loops)
• Model end-to-end (pick → LiveView active → LiveDoneMsg → Done)
• Global quit shuts down producer (verified bus is non-nil before, no panic on second cancel)
• Headless: happy path produces summary; bad scenario / zero duration / missing scenario all reject
• renderSnapshot mentions all key metrics
• `go vet`, `gofmt`, `gocyclo`, `gosec`, `golangci-lint` clean
• Smoke: `./inspect --scenario noisy --duration 500ms --yes` produces well-formed dashboard