Surface Studio Code payment-method requirement before the first prompt

[sejas]

Related issues

• Related to STU-2178: Surface credit card requirement before first Studio Code prompt
• Supersedes the visual prototype in Prototype Studio Code access requirements #4407

How AI was used in this PR

The visual design, copy, and illustration come from the human-reviewed prototype in #4407. This PR ports that design onto the real account checks; the result was reviewed and tested manually in both apps, in light and dark mode.

Proposed Changes

• Add gate screen when the user has no payment method added to their WPcom account.

Agentic UI	Classic

Testing Instructions

1. Log in with a WordPress.com account without a saved payment method.
2. Desktop classic tab: run npm start, open Studio Code — the payment requirement should replace the composer.
3. Agentic UI: run npm run cli:build:ui && node apps/cli/dist/cli/main.mjs ui --no-open, open http://localhost:8081 — opening a chat should show the same requirement instead of the composer.
4. Select Add payment method — the browser opens at https://my.wordpress.com/me/billing/payment-methods/add and Studio shows the waiting state.
5. Add a card, return to Studio, and select Check again — the chat should unlock into the normal conversation view.
6. With an entitled account, verify both chats load straight into the composer as before.
7. Go offline (or block the quota request) and verify the chats still open normally (fail-open).
8. Confirm layout and contrast in both light and dark mode.

The transition from the no-card state to the card state is immediate. Removing the card has a 5-minute cache.

Pre-merge Checklist

• Unit tests pass (npm test): gate, fail-open, hand-off, and re-check covered in both apps
• Type checks pass (npm run typecheck)
• Lint passes on modified files
• Verified visually in light and dark mode (classic tab and agentic UI)

[wpmobilebot]

📊 Performance Test Results

Comparing 2da719b vs trunk

app-size

Metric	trunk	2da719b	Diff	Change
App Size (Mac)	1402.83 MB	1402.85 MB	+0.02 MB	⚪ 0.0%

site-editor

Metric	trunk	2da719b	Diff	Change
load	1077 ms	1046 ms	31 ms	⚪ 0.0%

site-startup

Metric	trunk	2da719b	Diff	Change
siteCreation	7548 ms	7541 ms	7 ms	⚪ 0.0%
siteStartup	2887 ms	2867 ms	20 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)