fix: migrate from Svelte 4 lifecycle to Svelte 5

[rohanshrma222]

Description

Migrate legacy onMount/onDestroy lifecycle hooks and on:click event
handlers to Svelte 5 syntax ($effect and onclick).

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context.

Svelte 4 → 5 Migration (17 files)

• Converted onMount to $effect in 17 files
• Converted onDestroy cleanup to $effect return function
• Converted on:click to onclick in NutritionCalculator.svelte
• Added guards to prevent effects from running multiple times

Fixes #1000

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Checklist:

Author Self-Review:

• I have performed a self-review of my own code.
• I understand the changes I'm proposing and why they are needed.
• My changes generate no new warnings or errors (linting, console).
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Project	Deployment	Actions	Updated (UTC)
explorer	Ready	Preview, Comment	Feb 26, 2026 3:41pm