fix(wizard): polish custom-service form labels and step header

[kaiweijw]

Summary

• Add visible required-field markers (* plus aria-required) to Label, Endpoint URL, Auth method, and the dynamic credential label in the CLI Wizard's Custom / self-hosted service form. Optional fields (Custom slug, dynamic auth-key-name) are unchanged.
• Reset the Mode A wizard step header back to "Step 1 of 3 · pick a service" when the user clicks Back from the custom-service form. Previously the header was stuck at "Step 2 of 3 · enter credential" while the catalog grid was visible.
• Refresh the embedded wizard bundle hash so cli/tests/wizard_bundle_freshness.rs stays green.

closes #594
closes #603

Test plan

• cd frontend && npm run lint && npm run test && npm run build
• cd frontend && npm run build:wizard (verify the committed bundle hash is unchanged afterwards)
• cargo test -p nyxid-cli --test wizard_bundle_freshness
• Manual: nyxid service add --custom, confirm Label / Endpoint URL / Auth method / credential labels show * and the slug field stays "(optional)".
• Manual: switch Auth method to none, confirm the credential field disappears entirely.
• Manual: click Back from the custom form, confirm the header returns to "Step 1 of 3 · pick a service".