fix: allow move-up monitor transition with optional legacy maximize behavior

[martinmarth]

Summary

This PR fixes an issue where Move Window Up could not move windows to a monitor above when monitors are stacked vertically.

To preserve backward compatibility, it also introduces a setting that keeps the legacy behavior by default.

What was happening

In the keyboard move flow, UP could be consumed by local maximize logic before monitor-transition fallback was reached.
Result: DOWN worked, but UP often did not move the window to the monitor above.

Changes

• Added new setting key: always-maximize-with-up (default: true)
• Wired setting in Settings (KEY, getter, setter)
• Updated UP handling in tiling move logic:
  • maximize on UP only when:
    • always-maximize-with-up is enabled, or
    • there is no monitor in that direction (clamp)
• Added Preferences toggle:
  • Always maximize with Move Up

Behavior after change

• Default (unchanged): Move Up maximizes on current monitor.
• Optional: when the setting is disabled, Move Up transitions to monitor above (if available).
• Fallback: if no monitor exists above, Move Up still maximizes.

Files changed

• resources/schemas/org.gnome.shell.extensions.tilingshell.gschema.xml
• src/settings/settings.ts
• src/components/tilingsystem/tilingManager.ts
• src/prefs.ts

Testing

1. Arrange monitors vertically.
2. Keep setting enabled (default): verify Move Up maximizes.
3. Disable setting in Preferences: verify Move Up moves to monitor above.
4. Verify fallback: with no upper monitor, Move Up maximizes.

Closes #532