Move active surface between existing panes

[kyl33r]

Summary

• Add configurable commands for moving the active surface to the previous/next existing pane or to the pane on the left, right, above, or below.
• Route keyboard shortcuts, Command Palette actions, and View-menu commands through TabManager into the existing Workspace.moveSurface ownership-transfer path.
• Preserve the surface instance and focus, insert after the destination pane's selected surface, wrap previous/next traversal, and let Bonsplit collapse an emptied source pane.
• Reuse the same directional helper for existing tab-context-menu moves and clarify the old in-pane actions as “Reorder Surface Left/Right”.

All six new shortcut actions intentionally start unbound because the proposed Control-Command-arrow chords already belong to pane-focus actions. The actions remain discoverable and configurable in Settings and the Command Palette.

Scope

This is the focused existing-pane interaction slice from the movement proposal. It does not create panes or consolidate cross-workspace/window transfer.

Verification

• ./scripts/test-unit.sh -skipPackageUpdates test -only-testing:cmuxTests/MoveSurfaceBetweenPanesTests — 10 tests in 1 suite passed
• ./scripts/reload.sh --tag move-pane --launch — tagged Debug build succeeded and launched
• CMUX_TAG=move-pane scripts/cmux-debug-cli.sh list-workspaces — tagged socket responded
• swift build --package-path Packages/macOS/CmuxSettings
• scripts/lint-pbxproj-test-wiring.sh
• scripts/check-pbxproj.sh
• JSON validation for Resources/Localizable.xcstrings
• git diff --check
• swiftc -parse over changed Swift sources and the focused test file
• Complete live manual verification of terminal/browser state, pane wrapping, directional boundaries, focus, insertion order, and source-pane collapse

Test coverage added

• terminal and browser object identity/focus preservation
• insertion after the destination selected surface
• empty-source-pane collapse
• left/right/up/down movement and previous/next wrapping
• no-op behavior for missing destinations, Canvas layout, and remote-tmux mirrors
• settings/default/Command Palette metadata alignment
• physical-arrow shortcut routing through the production event handler

Closes #8752

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[kyl33r]

Superseded by #8845 after renaming the head branch to feat/8752-move-surface-between-panes as requested.