fix: remove unsupported email authentication

[sridharkalaibala]

Fixes #88.

Remove the email/password form, mode-switch controls, unused Zod schemas, and stub signIn/signUp methods from the auth context. Login and signup entry points retain their headings and offer Continue with Google. Correct both README and contributor setup instructions to configure Google OAuth and its allowed return URL.

Five tests render the actual modal with AuthProvider and the auth service, mocking only the Supabase client and toast boundary. They cover both entry modes, the existing Google provider/options and return URL, preservation of the pending route, disabled state while redirecting, and retry after returned or thrown OAuth errors. Before the fix, the two dead-form regressions fail and the three OAuth checks pass.

Validation: all 107 tests pass; typecheck and production build pass; lint passes with 26 existing warnings; git diff --check passes. The unchanged schema check passes in the LF validation worktree (the Windows checkout has unrelated CRLF schema drift). No schema or OAuth service/navigation code changed.

No live Google consent flow or production account was used. The tests verify the application request and preserved return-route state, not a live provider round trip. Prepared with AI assistance.

[strix-security]

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No security issues found.

_{Updated for 3e34dce.}

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[sridharkalaibala]

Thanks for reviewing and merging this, and the prompt image/text fixes in #122–#124.

[aashu2006]

Thanks, @sridharkalaibala! We really appreciate your interest in contributing 🙌

We’ve also added priority labels such as P0 and P1 to the issues. It would be great if you could take a look at those and consider working on them, as they are particularly valuable to the project.

[sridharkalaibala]

Thanks for pointing me toward the P0/P1 issues. I'll prioritize reviewing those next, check existing claims and PRs, and start with a focused issue I can reproduce and validate. I'll follow up on the selected issue with the proposed scope before starting.