feat(ai/runner): log live runner register and deregister events

[rickstaa]

What

Operator-visible logging for the live runner lifecycle. Previously the registry logged nothing on the happy path (only slog warnings/errors on failure), so "is my runner connected, and at what price?" had to be inferred from /discovery.

Dynamic runners

• live runner registered — new-runner branch of Heartbeat
• live runner deregistered — with a reason threaded from the call sites:
  • heartbeat timeout — expiry loop (crash, OOM, network loss, hard kill)
  • unregister — explicit SDK shutdown (graceful stop)

Static runners

• static live runner registered — first registration only (skips config reloads of an already-registered runner)
• static live runner health changed — only on ready <-> unavailable transitions (static runners can't heartbeat, so this is their up/down signal)

Pricing

• live runner price set — slog.Debug, fires on first set and on actual change (guarded so unchanged-price heartbeats stay quiet)

Levels

Lifecycle events are slog.Info; price is slog.Debug (config detail, also queryable via /discovery).

Note: go-livepeer doesn't yet wire slog's level to the -v flag, so slog.Debug is currently dormant. A follow-up PR to master will bridge slog's level to -v (repo-wide, also covers trickle/worker/media debug lines).

Notes

• The deregister log sits immediately after runner.removed = true, so it fires only when a removal commits, and every removal path funnels through that one chokepoint.

🤖 Generated with Claude Code

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[rickstaa]

@j0sh pushed this to draft since I might want to do some additional logging for the static path and display the initial price or price update.