feat(website): serve alchemy.run, redirect v2.alchemy.run to it

[sam-goodwin]

The v2 website takes over the apex domain. In prod the Worker attaches both hostnames, and a Single Redirect ruleset 301s v2.alchemy.run to alchemy.run at the edge (path + query preserved), so requests never reach the Worker:

domain: stack.stage === "prod" ? ["alchemy.run", "v2.alchemy.run"] : undefined,

const zone = yield* Cloudflare.Zone.Zone("Zone", { name: "alchemy.run" })
  .pipe(AdoptPolicy.adopt(true), RemovalPolicy.retain());

yield* Cloudflare.Ruleset.Ruleset("V2Redirect", {
  zone,
  phase: "http_request_dynamic_redirect",
  rules: [{
    expression: 'http.host eq "v2.alchemy.run"',
    action: "redirect",
    actionParameters: {
      fromValue: {
        targetUrl: { expression: 'concat("https://alchemy.run", http.request.uri.path)' },
        preserveQueryString: true,
        statusCode: 301,
      },
    },
  }],
});

• The zone is adopted (it predates this stack) and retained on destroy.
• Canonical site URL moves from v2.alchemy.run to alchemy.run: astro site, worker CANONICAL_HOST, llms.txt (regenerated), agent prompt, README, docs example.

Deploy order: https://github.com/alchemy-run/alchemy/pull/1448 must merge/deploy first — the Worker provider refuses to attach a hostname that is still attached to another Worker, and alchemy.run is currently on the v1 router Worker.

Also in this PR:

• Sweeps the remaining v2.alchemy.run references: Stack error message, AUTH_LANDING_HOST (/auth/success / /auth/error), migration-guide links to v1.alchemy.run, stale tutorial URLs in test comments.
• Preview-aware site URLs: the copy-for-agent prompt is built from window.location.origin after hydration, and the Worker rewrites llms.txt's baked canonical origin to the request origin on non-canonical hosts — PR previews now reference themselves instead of prod.
• Bumps distilled for fix(cloudflare/rulesets): putPhas redirect status_code is a number distilled#380 (putPhas redirect status_code is a number, not a string) — required for the V2Redirect ruleset to encode/decode. Merge that PR first so the submodule pointer lands on distilled main.

🤖 Generated with Claude Code

[alchemy-version-bot]

Install the packages built from this commit:

alchemy

bun add alchemy@https://pkg.ing/alchemy/51f36f1

@alchemy.run/better-auth

bun add @alchemy.run/better-auth@https://pkg.ing/@alchemy.run/better-auth/51f36f1

@alchemy.run/pr-package

bun add @alchemy.run/pr-package@https://pkg.ing/@alchemy.run/pr-package/51f36f1