fix(persistence): strict type validation for location/weather from localStorage

[Copilot]

Truthiness checks on parsed.location and parsed.weather allowed falsy invalid values ('', 0, false) to bypass validation and persist into app state.

Changes

• src/lib/core/persistence.ts: Replace truthiness guards with !== undefined + explicit typeof === 'string' checks before set/array membership tests; delete the key on any type mismatch or unrecognised value.

// Before — falsy values bypass the guard entirely
if (parsed.location && !LOCATION_IDS.has(parsed.location)) {
    delete parsed.location;
}

// After — any non-string or unrecognised value is rejected
if (parsed.location !== undefined) {
    if (typeof parsed.location !== 'string' || !LOCATION_IDS.has(parsed.location)) {
        delete parsed.location;
    }
}

Same pattern applied to parsed.weather. Consistent with how boolean flags are already validated in the same function.

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