fix(orchestrator): correct the deploy guidance — CF Workers Builds, no deco Admin flow

[JonasJesus42]

Follow-up to #332, which I got wrong.

What #332 got wrong

It added a Step 1 telling the user to go to admin.deco.cx → Sites → New Site. That flow does not exist — I inferred it from the symptom instead of checking, and it would have sent every non-dev user hunting for a page that isn't there.

It also described account_id / DECO_KV / SITES_KV / deco-otel-tail as "placeholders that become valid after registration". They aren't placeholders. deco-sites/storefront-tanstack's wrangler.jsonc ships real resources in deco's CF account:

"name": "storefront-tanstack",
"account_id": "c95fc4cec7fc52453228d9db170c372c",
"tail_consumers": [{ "service": "deco-otel-tail" }],
"kv_namespaces": [ { "binding": "DECO_KV", "id": "a205a78e..." }, ... ]

That distinction matters: a local wrangler deploy fails because the CLI isn't in that account, and deleting the keys until it succeeds is exactly what publishes the client's site onto whatever account the local token happens to own.

What this PR does

• Deploy setup is one manual step: CF dash → Workers & Pages → Create application → Connect to Git → pick the repo. The orchestrator asks for it up front instead of discovering it's missing after a 3-minute wait, and the prompt tells the user to check the account switcher.
• Keeps and re-grounds the ⛔ guard on wrangler deploy — now with the real reason.
• New Step 1 — rename the worker. template-bootstrap says "copy the tree, re-init git" and never touches name / DECO_SITE_NAME, so every migrated site currently deploys claiming to be storefront-tanstack. Found while verifying the above; shout if you'd rather split it out.

🤖 Generated with Claude Code

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Summary by cubic

Fixes the migration orchestrator's deploy instructions so users set up Cloudflare Workers Builds directly, instead of following a nonexistent deco Admin site flow.

• Removes the admin.deco.cx → Sites → New Site step; connecting the repo in the Cloudflare dashboard is now the one manual setup step.
• Adds a required first step to rename the worker from storefront-tanstack to the site slug in wrangler.jsonc.
• Clarifies that account_id, DECO_KV, SITES_KV, and deco-otel-tail are real resources in deco's Cloudflare account, and deleting them to force a local wrangler deploy can publish the site to whatever account the local token owns.

^{Written for commit 09ad339. Summary will update on new commits.}