fix: ignore Svelte script src imports

[BartWaardenburg]

Summary

• Svelte SFC markup-level <script src> references stay parsed as metadata but no longer emit synthetic imports.
• Vue external <script src> and SFC <style src> behavior stays unchanged.
• Added regression coverage for the reported SvelteKit <svelte:head> shape plus Svelte src variants.

Issue

Closes #835

Verification

• Minimal regression test for the reported SvelteKit head script.
• Real-world validation on a copied Knip SvelteKit fixture with <svelte:head><script src="/some-lib.min.js" async></script></svelte:head>: origin/main reports /some-lib.min.js, this branch does not.
• cargo check --workspace
• cargo test --workspace --all-targets
• cargo clippy --workspace --all-targets -- -D warnings
• cargo fmt --all -- --check
• cargo doc --workspace --no-deps --document-private-items
• typos .
• git diff --check
• fallow audit --format json --quiet (warn verdict from generated-file duplication unrelated to this Svelte change)