fix: add null/undefined guards for array access and navigation

- MasteryDisplay.svelte: Use optional chaining for split()[0] array access
  - formatRingStat().split('+')[0] -> split('+')[0]?.trim() ?? ''
  - formatEarringStat().split('+')[0] -> split('+')[0]?.trim() ?? ''
- TeamView.svelte: Same fix for formatAxSkill().split('+')[0]
- +layout.svelte: Add null guards for 'to' parameter and 'mainContent' in callback
  - Check !to before accessing to.url
  - Re-check !mainContent inside requestAnimationFrame callback

Fixes "Object is possibly 'undefined'" and "is possibly 'null'" errors with
noUncheckedIndexedAccess: true and strict null checks.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/lib/components/sidebar/details/TeamView.svelte

@@ -88,7 +88,7 @@
 			<ModificationSection title="AX Skills" visible={true}>
 				{#each weapon.ax as axSkill}
 					<StatModifierItem
-						label={formatAxSkill(axSkill).split('+')[0].trim()}
+						label={formatAxSkill(axSkill).split('+')[0]?.trim() ?? ''}
 						value={`+${axSkill.strength}`}
 						suffix={axSkill.modifier <= 2 ? '' : '%'}
 						variant="enhanced"

src/lib/components/sidebar/modifications/MasteryDisplay.svelte

@@ -46,7 +46,7 @@
 						{#if iconUrl}
 							<img
 								src={iconUrl}
-								alt={formatRingStat(ring.modifier, ring.strength, locale).split('+')[0].trim()}
+								alt={formatRingStat(ring.modifier, ring.strength, locale).split('+')[0]?.trim() ?? ''}
 								class="mastery-icon"
 							/>
 						{/if}
@@ -54,7 +54,7 @@
 					<span class="mastery-content">
 						{#if variant === 'detailed'}
 							<strong class="mastery-label">
-								{formatRingStat(ring.modifier, ring.strength, locale).split('+')[0].trim()}
+								{formatRingStat(ring.modifier, ring.strength, locale).split('+')[0]?.trim() ?? ''}
 							</strong>
 							<span class="mastery-value">
 								+{ring.strength}{getRingStat(ring.modifier)?.suffix || ''}
@@ -81,7 +81,7 @@
 					{#if iconUrl}
 						<img
 							src={iconUrl}
-							alt={formatEarringStat(earring.modifier, earring.strength, locale, characterElement).split('+')[0].trim()}
+							alt={formatEarringStat(earring.modifier, earring.strength, locale, characterElement).split('+')[0]?.trim() ?? ''}
 							class="mastery-icon"
 						/>
 					{/if}
@@ -89,7 +89,7 @@
 				<span class="mastery-content">
 					{#if variant === 'detailed'}
 						<strong class="mastery-label">
-							{formatEarringStat(earring.modifier, earring.strength, locale, characterElement).split('+')[0].trim()}
+							{formatEarringStat(earring.modifier, earring.strength, locale, characterElement).split('+')[0]?.trim() ?? ''}
 						</strong>
 						<span class="mastery-value enhanced">
 							+{earring.strength}{getElementalizedEarringStat(earring.modifier, characterElement, locale)?.suffix || ''}

src/routes/+layout.svelte

@@ -58,10 +58,11 @@
 
 	// Handle scroll restoration or reset after navigation
 	afterNavigate(({ from, to, type }) => {
-		if (!mainContent) return;
+		if (!mainContent || !to) return;
 
 		// Use requestAnimationFrame to ensure DOM has updated
 		requestAnimationFrame(() => {
+			if (!mainContent) return;
 			const key = to.url.pathname + to.url.search;
 
 			// Only restore scroll for browser back/forward navigation