Fix double canonical tag

src/routes/+layout.svelte:28 unconditionally emits <link rel="canonical"> from PROJECT_URL + pathname, while src/lib/Meta.svelte:84-86 also emits one when pageMeta.canonical is set. Pages overriding canonical end up with two tags.

Tasks

• Remove the unconditional canonical from +layout.svelte
• Have Meta.svelte always emit canonical, defaulting to PROJECT_URL + pathname when pageMeta.canonical is not set