fix(desktop): remove join API token control

[klopez4212]

Summary

Remove the nonfunctional API-token option from the existing-community join flow.

Validation

• Focused Playwright join-flow coverage
• Add-community screenshot coverage

[klopez4212]

🤖 Screenshots

Add a community

The flow begins with clear create and join choices.

Join an existing community

With a community URL entered, the token option is absent.

Create a new community

The create path remains unchanged.

[wesbillman]

Reviewing on Wes's behalf. No actionable findings at exact head 3d3d8629ab19529229d1c3d81ac2967b83b96e99.

This is a narrowly scoped UI/flow cleanup:

• The removed token was nonfunctional: the frontend could persist/pass it, but Rust apply_workspace does not declare a token parameter (desktop/src-tauri/src/commands/workspace.rs:127-133), so Tauri discarded it rather than applying it to relay authentication.
• URL/invite classification, bare-host normalization, join-policy discovery/acceptance, invite claiming, retry/error state, and Nostr-key connection paths are unchanged.
• The InviteRedeemForm call sites remain compatible: add-community narrows onConnect to its actual relay-URL contract; first-community already used that shape; membership recovery continues through onRedeem with its default relay.
• The test replacement positively covers both parts of the intended behavior: the token controls are absent after entering a valid URL, and submitting that URL still persists the expected onboarding transaction. Existing invite, policy, and deep-link lanes remain intact.
• Removing the optional reveal/password controls only removes dead tab stops; the form, autofocus input, Enter submission, back/cancel behavior, and visible layout remain intact. The updated screenshot confirms the intended compact flow.

All listed Desktop, Playwright, build, DCO, and guard checks are green; the PR is mergeable. I consider this safe to merge.