Remove Unconfirmed default tag from Zetkin signups

[conatus]

Summary

• Removes the hard-coded $addTags[] = "Unconfirmed"; line in ZetkinService::addPerson that tagged every newly created Zetkin person with "Unconfirmed"
• Bumps plugin version to 1.4.3 (readme.txt, join.php, index.tsx Sentry release)

Context

The default tag was applied unconditionally inside the token-based addPerson flow, independent of the per-plan add_tags / remove_tags configuration and the ck_join_flow_add_tags / ck_join_flow_zetkin_add_tags filters. New Zetkin records will no longer receive this tag automatically. Tags supplied via membership plan config or filters continue to work unchanged.

No existing tests in packages/join-block/tests/ covered this behaviour, so no test updates were required.

Test plan

• Deploy 1.4.3 to staging
• Submit a join-flow signup wired to Zetkin with token credentials configured
• Confirm the new Zetkin person is created without an "Unconfirmed" tag
• Confirm tags from membership plan add_tags and from ck_join_flow_add_tags filter hooks are still applied
• Confirm remove_tags still apply correctly
• Promote to production once staging verified