feat: floating panels — center-area overlay support

[sandesh-sp]

Closes #99

Summary

• Rendering: Six anchor positions (float-top-left/center/right, float-bottom-left/center/right) rendered as absolutely-positioned, transparent overlay zones inside the center map area — map stays fully visible through gaps between tool cards.
• Validator: Enforces at most one float panel per position; floatingPanels accepted as a separate array from edge panels.
• State guard: PanelManager_.setPanelState now rejects iconified and focused transitions for float panels at runtime, with a clear error message.
• Corner radius: Moved border-radius from the transparent .ui-float-panel container to .ui-float-panel .ui-tool-card where it has visual effect; compact mode resets to border-radius: 0; added padding and overflow: hidden so corners are visibly clipped.
• FLOAT_POSITIONS deduplication: Removed the local redeclaration in UserInterfaceModern_.js; now imported from the canonical PanelManager_/types/layout.ts.
• Configure UI: Fixed incorrect description ("Multiple panels at the same position stack vertically" contradicted the one-per-position rule); removed the irrelevant priority field from the Floating Panels section.

Test plan

• Configure a floating panel at each of the six positions and confirm it renders on top of the map at the correct anchor with the map visible through gaps.
• Configure two floating panels at the same position and confirm a validation error is thrown.
• Attempt to set a float panel state to iconified or focused and confirm an error is thrown.
• Set maxHeight on a float panel and verify the body scrolls when tool content exceeds it.
• Confirm tool cards have rounded corners in overlay mode and square corners in compact mode.
• Open the Configure page → UI tab → Floating Panels section and confirm: only float positions in the dropdown, only collapsed/expanded state options, no priority field.

[github-actions]

✅ Version Already Updated

This PR includes a manual version update to 4.2.11-20260611

No automatic version bump needed.