Release v0.6.3

fix: restore header version positioning (#41)

## Problem
The previous header interaction fix accidentally made every
`.app-header-actions` container `position: relative`, which overrode the
absolutely positioned version/update cluster and pushed it into the
normal header layout.

## Approach
Keep the header stacking fix intact, but remove the global positioning
override from `.app-header-actions` so the version and update controls
remain anchored to the top-right while still using the no-drag region
for clicks.

## Scope
- Restore the header version/update cluster positioning
- Preserve the update button interaction fix
- Bump the Tauri app version to 0.6.3 with the existing Makefile target