Ask about demo data when creating a dev store interactively

[nickwesselman]

WHY are these changes introduced?

shopify store create dev can already populate a new store with demo data through
--with-demo-data, but nothing ever asks about it. A developer creating a store
interactively — including through the inline creation flow that #8323 and #8397 just
added to app dev — gets an empty store and no indication that demo data was an
option.

WHAT is this pull request doing?

Adds a demo data question to interactive dev store creation, asked after the name and
plan prompts.

• New shared devStoreDemoDataPrompt in @shopify/organizations, next to the existing
  name and plan prompts, re-exported as storeDemoDataPrompt (store) and
  devStoreDemoDataPrompt (app) through the same thin delegates those two already use.
  "Yes, add demo data" is preselected.

• store create dev gives the flag the standard tri-state behavior. --with-demo-data is
  renamed to --demo-data and gains allowNo, so:

  // An unspecified flag means "ask" where we can prompt and "no" where we can't.
  const withDemoData = flags['demo-data'] ?? (terminalSupportsPrompting() ? await storeDemoDataPrompt() : false)

  --demo-data and --no-demo-data answer the question outright and skip the prompt. An
  unspecified flag prompts in an interactive terminal and defaults to false in a
  non-interactive one, using the same terminalSupportsPrompting() check that
  requiredIfNonInteractive enforcement uses. SHOPIFY_FLAG_STORE_DEMO_DATA counts as
  specified, so it also skips the prompt.

• app dev has no demo data flag and rejects non-TTY runs upstream, so it always asks,
  on both the zero-store and store-picker creation paths.

One note for reviewers: --with-demo-data is renamed rather than aliased. The command is
hidden, and the flag only reached main alongside the unreleased inline creation work, so
no documented workflow should depend on the old spelling. Say the word if you would rather
keep --with-demo-data as a hidden alias.

How to test your changes?

1. shopify store create dev --organization-id <id> --name test-store --plan basic in a
   terminal — asks "Populate the store with demo data?" with Yes preselected.
2. Same command with --demo-data or --no-demo-data — no question, and the created store
   reflects the flag.
3. Same command piped from another process (or with CI=1) — no question, demo data off.
4. shopify app dev --reset in an App Management organization, then either accept the
   zero-store creation flow or pick "Create a new dev store" from the picker — name, plan,
   then the demo data question, and the created store reflects the answer.

Tophat: the app dev path was exercised locally end to end (name, plan, demo data
question, store created, dev started). The store create dev flag-gating paths are
covered by unit tests but were not live-tophatted.

Changelog

No changeset. This builds on the inline dev store creation from #8323 and #8397, which is
not released yet, so the whole flow will be covered by a single changelog entry rather than
one per PR in this stack.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add — intentionally omitted, see Changelog above

[amcaplan]

The CLI defaults to no demo data; it's an opt-in. Here it's phrased as an opt-out. Do we want to align the two experiences?

[nickwesselman]

I think we should encourage new users to use it.

[amcaplan]

I'm ambivalent about the whole idea, but I can live with it.

[github-actions]

⚠️ Potential Breaking Changes Detected

This PR contains changes that may break the existing contract.

@shopify/dev_experience — this PR contains breaking changes that require coordination for the next major release.

🏳️ Removed Flags

The following flags were removed from existing commands:

Command	Flag
store:create:dev	--with-demo-data

🔧 Removed Environment Variables

The following env vars are no longer referenced in command flags:

Env Var	Previously Used By
SHOPIFY_FLAG_STORE_WITH_DEMO_DATA	store:create:dev --with-demo-data