Fix onboarding wizard step navigation

[saltyyboii]

What this changes

Fixes #659. Corrects the Launch screen's Fix buttons so that Repositories navigates to wizard step index 2 and Projects navigates to step index 3, accounting for the Email step. Updates the test to verify the correct navigation indexes.

AI-assisted contribution: I used ChatGPT to help investigate the issue and update the implementation and test. I reviewed the changes and ran the tests locally.

Evidence

$ cd web && node --test src/onboardingProjects.test.mjs
ℹ tests 33
ℹ suites 0
ℹ pass 33
ℹ fail 0
ℹ cancelled 0
ℹ skipped 0
ℹ todo 0

$ python scripts/check_release_manifest.py --strict
OK: 1736 file(s) match RELEASE_MANIFEST.txt

Checklist

• Tests cover the change, and they fail on the unfixed code.
• Test count and assertion count did not go down, or the PR body explains why.
• Lockfiles committed if a dependency changed.
• Nothing in the diff reads or writes a credential inside the repo.
• AI-assisted portions are disclosed above, and I can defend every line.
• Suite run locally; command + output tail pasted under Evidence.
• This does not conflict with the project's standing constraints.
• First PR only: I have read CLA.md and added my contributors/saltyyboii.md entry to this PR.