feat: add crypto payment options to dashboard Stripe modal (CPL-274)

[GTC6244]

Summary

Switches the Add Funds modal in the dashboard from Stripe's Card Element to the Payment Element, which auto-renders whichever methods are enabled on the Stripe account (card + crypto: USDC, USDP, ETH, SOL). Backend billing endpoints already support crypto — this is a frontend-only change.

Linear: CPL-274

What changed

• lit-static/dapps/dashboard/index.html — Billing modal split into a two-step flow: amount selector + Continue (step 1), then Payment Element mount point + Back/Pay (step 2). stripe-card-element renamed to stripe-payment-element.
• lit-static/dapps/dashboard/billing.js — Rewrote the payment flow. Continue creates the PaymentIntent and mounts elements({ clientSecret }).create('payment'). Pay calls stripe.confirmPayment({ elements, confirmParams: { return_url }, redirect: 'if_required' }) — card stays inline, crypto redirects to the wallet flow. Exports new handleBillingReturn() that detects ?payment_intent=…&redirect_status=… on page load, calls the backend confirm_payment endpoint, and strips the query params.
• lit-static/dapps/dashboard/app.js — Imports and invokes handleBillingReturn() from the setOnAuthReady callback so the crypto-redirect return is processed once the API key is loaded.

Why

The existing modal used elements.create('card') + confirmCardPayment(), which is card-only and doesn't surface Stripe's crypto options. The Payment Element approach is a minimal frontend refactor that unlocks card + crypto in one UI — no backend changes needed.

Pre-Landing Review

No blocking issues found.

• Security/data safety: return_url is built from window.location.origin + window.location.pathname (no user input). Status display uses textContent (no XSS surface). No new credentials/tokens exposed.
• Error handling: handleContinue, handlePay, and handleBillingReturn all wrap network calls in try/catch. confirmPayment-backend failure preserves the prior "card charged, credit pending" fallback. URL params stripped before confirm_payment call so reloads don't retrigger.
• Edge cases checked: double-click on Continue/Pay (buttons disabled in-flight, re-enabled in finally); amount change mid-flow (Back fully unmounts the element, next Continue creates a fresh intent); repeated handleBillingReturn calls (URL cleaned first, subsequent fires no-op); Stripe account without crypto enabled (Payment Element gracefully shows card only).

Test plan

Requires a dev backend with Stripe test keys and a Stripe account that has crypto payment methods enabled.

• Open dashboard → Add Funds → amount step shows with dropdown + Continue
• Pick $5 → Continue → Payment Element renders with card (and crypto tabs if enabled)
• Back button returns to amount step (unmounts element; next Continue creates a fresh PaymentIntent)
• Card path: submit test card 4242… → stays inline → balance updates → modal closes
• Crypto path: select crypto → connect wallet → approve → redirects out → returns to dashboard root → auth ready fires → handleBillingReturn calls confirm_payment → overview shows "Credits added" → balance refreshes
• Confirm that an unauthenticated user hitting ?payment_intent=… silently strips the params without processing (no crash, no retry loop)

Notes

• No unit tests exist for the vanilla-JS dashboard module — node --check passes on both JS files.
• Crypto docs at docs/management/crypto.mdx already describe the intended user flow and reference the Payment Element approach this PR implements.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Updates the dashboard “Add Funds” modal to use Stripe’s Payment Element so enabled payment methods (including crypto) can be used in a single flow, and adds return-handling for redirect-based methods.

Changes:

• Replaced the Card Element UI with a two-step modal (amount → payment) and a Payment Element mount point.
• Reworked the billing flow to create a PaymentIntent on “Continue” and confirm via stripe.confirmPayment(..., redirect: 'if_required') on “Pay”.
• Added handleBillingReturn() and wired it into the auth-ready callback to confirm redirect-based payments on return.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
lit-static/dapps/dashboard/index.html	Updates modal markup for a two-step flow and Payment Element container/buttons.
lit-static/dapps/dashboard/billing.js	Implements Payment Element flow, confirm logic, and redirect-return processing.
lit-static/dapps/dashboard/app.js	Calls handleBillingReturn() after auth is ready so redirect returns are processed.

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[glitch003]

looks solid