Admin bar: floating chat panel across every wp-admin screen

[lezama]

Summary

Adds a global floating chat panel reachable from a toolbar item on every wp-admin screen. Click the chat icon in the admin bar → a slide-in drawer opens on the right edge with the same chat surface as the wp-admin → openclaWP → Chat page.

• Hooks: admin_bar_menu for the toolbar item, admin_enqueue_scripts for the panel script, admin_footer for the React mount point + inline toggle bridge.
• Reuses @automattic/agenttic-ui (<AgentUI>) and @wordpress/components (Button, Notice, SelectControl) — no new dependencies.
• Extracts the inner chat surface into blocks/chat-shared/ChatSurface.jsx so the block view and the panel view share one component (tool-call confirmation, session handling, agent picker).
• Drawer open/closed state persists in localStorage (openclawp:panel:open) so the panel re-opens on page nav. Esc closes.
• Gated on manage_options for v1; an openclawp_admin_bar_panel_enabled filter lets hosts switch it off.
• Same agent-filtering rules as the chat block (workflow drafter excluded; openclawp_chat_block_agents filter respected).

Why

Today openclaWP's chat only lives at /wp-admin/admin.php?page=openclawp — you have to navigate there to talk to the agent. The floating panel makes the agent reachable from any admin context (editing a post, browsing plugins, etc.), which is the surface a regular admin actually uses.

Test plan

• Open any wp-admin page. The chat icon appears in the admin bar (right-side, before the user menu).
• Click the icon. A drawer slides in from the right edge with the chat UI.
• Send a message; the agent responds the same way the existing block does.
• Close and re-open the panel — conversation persists.
• Navigate to a different admin page — the panel re-opens if it was open before.
• Press Esc while the drawer is open — it closes.
• Set the openclawp_admin_bar_panel_enabled filter to false — the toolbar item disappears.
• Tool-call confirmation card still works inside the panel (any gated ability the agent tries to call surfaces the Allow/Deny/Always-allow UI).
• Existing Chat page (/wp-admin/admin.php?page=openclawp) still renders identically — the shared component extraction didn't regress.

Verified locally

• npm run build — all bundles emit cleanly.
• npm run lint — clean.
• vendor/bin/phpunit --testsuite unit — 169/169 (was 169, no regression).

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