feat(ui,infra): SvelteKit ui scaffold, Makefile, pre-commit, claude hooks

ui/: SvelteKit 2 + Svelte 5 + Tailwind 4 + shadcn-svelte (luma, lucide)
on bun with ultracite; adapter-static with SPA fallback; theme tokens
taken from msos. Dockerfile gains a bun stage that builds ui/build.
Makefile and pre-commit cover ruff, ty, ultracite and svelte-check;
.claude settings run the matching fixer after edits. docs/PRODUCT.md
captures product truth for the UI work.

ui/src/routes/+page.svelte

@@ -0,0 +1,5 @@
+<h1>Welcome to SvelteKit</h1>
+<p>
+  Visit <a href="https://svelte.dev/docs/kit">svelte.dev/docs/kit</a> to read
+  the documentation
+</p>