Add trading dashboard welcome guide

[Sikkra]

Closes #13.

Summary

• Adds a first-run trading dashboard welcome modal with concise CAP onboarding steps.
• Includes bridge, wallet connect, docs, and start-trading actions.
• Adds a persistent Guide entry in the chart toolbar so users can reopen the modal any time.
• Keeps the Guide action available while candles are loading by only disabling resolution controls during chart loading.

Verification

• npm ci
• npm run build
• Browser smoke check on local build: first-run modal renders at /trade/ETH-USD; local geofence overlay in this environment prevents full pointer verification of the underlying toolbar, but the modal contents and Guide control are present in the DOM with no browser console errors.