Auth: make profile upsert on signup fatal (no silent user-without-profile)

[syed-reza98]

Why

Docs note AuthRepository.signUp treats profile upsert failure as non-fatal, which can create users with incomplete profile rows.

Current behavior

• User can register successfully, but profiles row may be missing if insert/upsert fails.

Tasks

• Update signup flow so profile creation failures surface to user and block completion
• Ensure error is user-friendly and actionable (retry)
• Add logging/metrics if available

Acceptance criteria

• Registration fails if profile row cannot be created
• App does not proceed into authenticated state with missing profile

References

• docs/01_CODEBASE_ARCHITECTURE_REVIEW.md: “Profile Upsert Non-Fatal Error”
• docs/02_FEATURES_REQUIREMENTS_BEST_PRACTICES.md: Auth issues section

[syed-reza98]

Closed as completed via PR #71.