feat: wire create/claim/cancel buttons to the real pool flow

[sainathr19]

Summary

The "act on this plan" buttons only ever called the devnet demo writer — pool mode just showed a static "not wired yet" message. Wires them to strk20.js's real create/claim/cancel (the Wallet API route from #20).

• strk20.js: createPlan/claim/cancel now resolve in_token/out_token internally (one cached view call per contract address) instead of requiring the caller to already know them — matches devnet-writer.js's existing viewCall convention, and lets App.jsx's demo and pool code paths share the same params shape.
• App.jsx: buttons are now gated on demoMode OR an actually-detected, STRK20-capable wallet (detectPrivacyCapable from feat: switch real pool flow to the Wallet API route, unblocking mainnet #20) rather than just "not demo mode" — so the button's enabled state matches what a click would actually do, never promises something that immediately fails.

Test plan

• vite build succeeds
• npm test (ui) — 4/4 pass (unaffected, doesn't touch iceberg.js)
• Not verified: an actual live Ready wallet clicking these buttons end to end — still no such environment available here. This is the last piece of code before the required mainnet transactions can happen through the real UI; needs a human test before relying on it for those.