[audit] Add SQLite characterization tests for mutable repositories

[bnema]

Summary

Several mutable SQLite repositories have no direct repository-level characterization tests.

Why this matters

Usecase-heavy tests mock these repos, so SQLC mapping bugs, null handling issues, transaction mistakes, or persistence regressions can slip through.

Evidence

• internal/infrastructure/persistence/sqlite/favorite_repo.go
• internal/infrastructure/persistence/sqlite/permission_repo.go
• internal/infrastructure/persistence/sqlite/session_state_repo.go
• internal/infrastructure/persistence/sqlite/zoom_repo.go
• Nearby direct tests exist for history, favicon, and session repos, but not for these mutable repos.

Suggested scope

• Add direct repository tests for favorites/folders/tags, permissions, session state, and zoom levels.
• Cover create/update/delete/list flows, null fields, duplicate/constraint behavior, and transaction boundaries.
• Reuse existing temp-DB migration helpers where possible.

Acceptance criteria

• Each mutable repo has at least one direct round-trip test suite.
• Transactional and null-handling behavior is covered where relevant.
• The new tests run in the normal repository test command.

Audit context

• Audit date: 2026-06-10
• Audited at commit: 5eba8fd5