Dashboard: full-height expand bar when panel is collapsed

[waleedkadous]

Problem

When the architect panel is collapsed, there's only a small "Expand" button in the app header. Same when the work panel is collapsed. There should be a full-height clickable bar along the collapsed edge (left side for architect, right side for work panel) that the user can click to expand.

Expected Behavior

• When architect panel is collapsed: full-height vertical bar on the left edge — clicking it expands the architect panel
• When work panel is collapsed: full-height vertical bar on the right edge — clicking it expands the work panel
• These should be obvious/visible affordances, not subtle

Context

Follow-up to #522 (toolbar consolidation). The toolbar is now unified, but the expand affordance when collapsed needs to be a full-length bar, not a small header button.

[waleedkadous]

On it! Working on a fix now.

[waleedkadous]

Additional Requirement: Tri-state collapse button

When a panel is fully expanded (the other panel is collapsed), showing "Expand left" and "Expand right" buttons is wrong. There should be one button with tri-state behavior:

Collapse architect button (in toolbar):

1. First click: collapse architect → 50/50 split (if architect was full-width)
2. If already 50/50: collapse architect → full work panel

Collapse work button (in toolbar):

1. First click: collapse work → 50/50 split (if work was full-width)
2. If already 50/50: collapse work → full architect panel

In other words: the button cycles through states, not two separate expand/collapse buttons.

[waleedkadous]

Additional Requirement: Color-coded connection status

The connection status indicator in the toolbar should use traffic-light colors:

• Green: Connection healthy, everything working
• Yellow: Minor disruption — reconnecting, brief interruption, unstable
• Red: Major disruption — disconnected, connection lost, unable to reconnect

Should be immediately obvious at a glance.