feat: improve account admin filters and bulk model inputs

[zjarlin]

Summary

• add saved account filter tabs with URL query-string persistence so admin account filters survive refresh/share links
• support schedulable filtering plus default display-group, name-prefix, and regex-driven search presets on the account list
• replace single-line model whitelist editing with multiline bulk input, and add multiline bulk import for model mappings in create/edit account forms
• keep the account-admin data/API layer aligned with the new filters and bulk input workflow

Notes

• separated from fix: show scheduled accounts in ops and threshold temp unscheduling #2244 on purpose so ops/scheduler fixes and account-admin UI changes can be reviewed independently

Testing

• go test -tags unit ./internal/handler/admin
• go test -tags unit ./internal/service -run 'TestAdminService_ListAccounts_WithSearch|TestAdminService_ListAccounts_WithPrivacyMode|TestAdminService_ListAccounts_WithNamePrefix|TestAdminService_ListAccounts_WithSchedulableFilter|TestAdminService_ListAccounts_ExhaustedCodexExtraDoesNotSetRateLimit'
• pnpm build

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