Authentication Foundation and Session Hardening

• refactored auth modules for clearer responsibilities
• expanded auth-oriented test coverage for core account flows
• prepared auth hooks for downstream product modules

• initial authentication foundation for the product shell
• account confirmation and password reset flow support
• improved session lifecycle handling

This release introduces a stronger authentication baseline for Modlith, including cleaner account flows and safer session handling defaults.

• resolved edge cases around stale session state after auth events
• improved error handling for invalid confirmation and reset tokens

• simplified onboarding path for first-time users
• clearer auth-related UI states for sign in and verification
• reduced auth boilerplate in controller and LiveView integrations