feat: add message metadata viewer on hover

Small info button appears on hover of each message bubble.
Click to expand a panel showing raw message metadata (id, role,
timestamp, channel, sender info, etc.) from the gateway.
Useful for debugging and understanding message routing.
Collapsed by default, doesn't clutter the UI.

Closes feedback item #39

FEEDBACK.md

@@ -479,3 +479,14 @@
   - Could use a lighter background (slightly brighter than assistant messages) or a colored left border
   - Keep it subtle but clearly distinguishable
   - Test against the zinc dark theme to make sure it's readable for keratoconus (no harsh contrast)
+
+## Item #45
+- **Date:** 2026-02-12
+- **Priority:** high
+- **Status:** pending
+- **Description:** Display the agent's avatar when set in OpenClaw config
+  - OpenClaw gateway can provide an avatar URL for the agent (configured in openclaw.json)
+  - PinchChat should display this avatar next to assistant messages instead of the default Bot icon
+  - Check the gateway WebSocket session/handshake data for avatar info
+  - Fallback to the current default icon if no avatar is configured
+  - Should also appear in the header next to the agent name