feat(gui): visual block groups with nested navigation and boundary wiring

[LukasikMaxence]

Summary

Introduce visual block groups in the diagram editor: containers that organize the GUI without changing the simulation graph (diagram blocks/connections stay unchanged).

• Group / ungroup selected blocks and nested sub-groups (Ctrl+Shift+G / Ctrl+Shift+U)
• Navigate into groups (double-click) with breadcrumb bar: member layouts saved per view level
• Auto boundaries derived from wires crossing group borders:manual In/Out proxies for partial wiring
• Partial boundary wiring: delete/reconnect one side at a time with dashed --- wires; undo/redo throughout
• Nested groups (parent/child hierarchy), cross-group connections, proxies for child boundaries inside parent view
• Ctrl+R flips group rectangle and In/Out proxy display without rotating member blocks
• Copy/paste of blocks, nested groups, and manual In/Out proxies
• Persistence under gui.groups in project.yaml (simulation export unchanged)
• Example examples/basics/nested_groups (ControlLoop with Regulator / Plant)
• Gui tests dedicated to groups

Wire routing fixes

• Manual routes preserved when moving blocks at the same view level
• Manual routes recomputed when entering another group view or when anchor redirection changes
• Dashed boundary wires follow group/proxy/block moves
• Undo of connection delete no longer duplicates Out proxies

Also included

• Preserve per-panel series styles when enlarging manual plot preview
• Preserve manual plot zoom when switching active panel