fix(NcAppNavigation): deactivate focus on resize

[Antreesy]

☑️ Resolves

• Fix case when isMobile changed true -> false with open: true was never considered, and trap stayed active

Reproduction steps:

1. Load the app on ≥ 1024px — isMobile = false, open = true
2. Resize window to below 1024px — isMobile = true → watch(isMobile) fires → open changes from true to false → watch(open) fires → toggleFocusTrap() called, trap deactivates
3. Open the navigation on mobile — open = true → watch(open) fires → toggleFocusTrap() called → isMobile=true && open=true → trap activates
4. Resize back to ≥ 1024px — isMobile = false → watch(isMobile) fires → sets open.value = !false = true.

• open was already true → Vue sees no change → watch(open) does NOT fire.
• toggleFocusTrap() is never called.
• Focus-trap remains active on desktop. ← BUG

🚧 Tasks

• Manual tests:
  Bug is happening sometimes on production, so far it's the only reliable steps to reproduce it

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 2️⃣ Backport to stable8 for maintained Vue 2 version or not applicable

[Antreesy]

stable8 has this handler in both watchers, so backports are not needed:

	watch: {
		isMobile(value) {
			this.open = !value
			this.toggleFocusTrap()
		},

		open(value) {
			this.toggleFocusTrap()
			emit('navigation-toggled', {
				open: value,
			})
		},
	},
	```

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.06%. Comparing base (65a6f32) to head (c05b977).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8646      +/-   ##
==========================================
+ Coverage   54.02%   54.06%   +0.04%     
==========================================
  Files         106      106              
  Lines        3478     3479       +1     
  Branches     1008     1008              
==========================================
+ Hits         1879     1881       +2     
+ Misses       1355     1354       -1     
  Partials      244      244              

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