feat(hub): expose panel session lifecycle events

[dvcolomban]

Summary

• expose live dock-panel connected, changed, and disconnected events with server-minted RPC session IDs
• add the framework-neutral reportDockPanelState client helper and wire restored initial state plus later transitions in both built-in clients
• deduplicate reports per connection and compose disconnect cleanup with the existing RPC peer lifecycle
• document the bus and RPC event names and update the public API snapshots

The existing $bindState and on.change contract already supports consumer-owned tab persistence through RPC actions, so this intentionally includes no tabs API change.

Dependency

This branch is based on codex/fix-edge-dock-refresh so the initial hub-ui report observes restored panel state. Rebase it onto main after that fix lands.

Testing

• pnpm lint
• pnpm knip
• pnpm test
• pnpm typecheck
• pnpm build

Part of #229.

[vercel]

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