feat: auto-convert camelCase property names to snake_case column names

[markshust]

Summary

• Auto-conversion: EntityMetadataFactory now converts camelCase property names to snake_case column names when no explicit name: is provided on #[Column] (e.g., $createdAt -> created_at, $userId -> user_id)
• Edge cases handled: consecutive caps ($userID -> user_id), leading acronyms ($HTMLParser -> html_parser), single-word properties unchanged
• Explicit override preserved: #[Column(name: 'custom')] still takes priority
• Boilerplate removed: ~30 redundant explicit column names removed from production entities across admin-auth, media, webhook, and authentication-token packages
• FK names improved: now use snake_case (fk_posts_user_id instead of fk_posts_userId)
• Docs updated: convention documented in database package docs and all tutorials

Breaking change: existing databases with verbatim camelCase column names will need migration or explicit name: overrides.

Test plan

• New tests for camelCase-to-snake_case conversion edge cases
• Existing override test updated to use genuinely custom name (not matching auto-conversion)
• All database package unit tests updated and passing
• All database package feature tests updated and passing
• All Repository tests updated and passing (23 isActive refs migrated)
• All admin-auth, media, webhook, authentication-token entity tests updated and passing
• Full test suite passing (4462 tests)
• Standards enforcer run on all changed files
• Documentation updated across guides, tutorials, and READMEs

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