[Enhancement] Use better-auth modelName and fields mapping for ObjectQL adapter (snake_case compatibility)

[hotlong]

Context

Currently, the ObjectQL adapter for better-auth passes field names as-is from better-auth's camelCase queries to ObjectStack's snake_case database schema. This causes query failures (e.g., login, account lookup) when field names don't match (see Bug #893).

Proposal

Implement Approach B: declare model/field mapping in the better-auth configuration using its official modelName and fields options for each core auth model.
需要考虑所有插件用到的表，包括org等

Details

Instead of runtime camelCase ↔ snake_case conversion in the adapter, leverage better-auth's documented schema customization:

export const auth = betterAuth({
 user: {
 modelName: "sys_user",
 fields: {
 emailVerified: "email_verified",
 createdAt: "created_at",
 updatedAt: "updated_at",
 },
 },
 session: {
 modelName: "sys_session",
 fields: {
 userId: "user_id",
 expiresAt: "expires_at",
 ipAddress: "ip_address",
 userAgent: "user_agent",
 createdAt: "created_at",
 updatedAt: "updated_at",
 },
 },
 account: {
 modelName: "sys_account",
 fields: {
 userId: "user_id",
 providerId: "provider_id",
 accountId: "account_id",
 accessToken: "access_token",
 refreshToken: "refresh_token",
 idToken: "id_token",
 accessTokenExpiresAt: "access_token_expires_at",
 refreshTokenExpiresAt: "refresh_token_expires_at",
 createdAt: "created_at",
 updatedAt: "updated_at",
 },
 },
 verification: {
 modelName: "sys_verification",
 fields: {
 expiresAt: "expires_at",
 createdAt: "created_at",
 updatedAt: "updated_at",
 },
 },
});

This ensures better-auth always uses the correct field names for data persistence and querying via ObjectQL.

Benefits

• Single-point schema mapping, no runtime conversion
• Cleaner adapter logic
• Official/documented API usage
• Reduces risk of edge-case bugs

Tasks

• Add modelName and fields for all core models in better-auth config
• Update auth-manager.ts to construct config accordingly
• Review/adjust adapter and tests as needed
• Validate sign-in, sign-up, and all account workflows
• Document the mapping approach in README

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相关问题: #893