Redesign Agents page: compact table with actions menu

[wesbillman]

Summary

• Replace verbose per-agent cards with a clean, scannable table (name, status, model, runtime, actions menu)
• Move all agent actions (spawn/stop, add to channel, mint token, copy pubkey, view logs, auto-start, delete) into a 3-dot dropdown menu per row
• Auto-discover models on render instead of requiring a manual "Discover models" button click
• Remove relay URL and auth info from the view — static config that wasn't actionable
• Delete unused ManagedAgentCard component and formatTimestamp helper
• Normalize border radius from rounded-3xl to rounded-xl to match the rest of the app

Test plan

• Verify the managed agents table renders correctly with 0, 1, and multiple agents
• Verify all 3-dot menu actions work: spawn, stop, add to channel, mint token, copy pubkey, view logs, enable/disable auto-start, delete
• Verify model picker auto-loads and allows switching models
• Verify the relay directory table still renders correctly
• Verify the log panel populates when "View logs" is selected from the menu

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