cli/dx: verify and harden node_modules missing hint for Hosted

[CodewithJha]

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Context

First-time Hosted can fail obscurely without npm install. scripts/dev.sh already prints tip: cd apps/web && npm install when apps/web/node_modules is missing. docs/COLD_START.md and README Troubleshooting also mention it. This issue is a verify / harden pass, not a greenfield feature.

Goal

Confirm the tip is visible on a clean tree; improve the message and/or docs only if something is still easy to miss.

Why it matters

Hosted is optional, but when someone runs ./scripts/dev.sh without Node deps, a clear tip saves a support thread.

Acceptance criteria

• Confirm tip appears when apps/web/node_modules is absent (rename/move the folder briefly, run ./scripts/dev.sh, restore)
• If the tip is easy to miss (scroll, timing, wording), improve scripts/dev.sh and/or COLD_START / README Troubleshooting
• No Hosted UI redesign
• PR links this issue or comment with evidence (screenshot/log of tip) + “already sufficient” and close

Suggested files

• scripts/dev.sh
• Possibly docs/COLD_START.md, README.md Troubleshooting

Out of scope

• Auto-running npm install inside dev.sh, changing Node version requirements, frontend build pipeline

Hints

• Tip today is printed just before npm run dev — check whether a failed npm still leaves the tip visible in the terminal scrollback.
• Prefer a slightly louder one-liner over new docs pages if COLD_START/README already cover install.
• Closing with evidence is a valid outcome.

Difficulty

XS · scripts / docs

Docs

• Catalog: GOOD_FIRST_ISSUES.md #24
• COLD_START.md