feat: add OpenAI account request overrides and proxy-based admin/group controls

[is7Qin]

Summary

This PR mainly introduces three feature areas:

• feat: add OpenAI account request overrides
• feat(group): add proxy-bucket load balancing
• feat(admin): add proxy filter for account list

Changes

OpenAI account request overrides

• add account-level request overrides for OpenAI accounts
• allow admins to define custom request parameters that override client-supplied values before forwarding upstream
• support configuring these overrides in account management flows

Group-level proxy-bucket load balancing

• add the group-level proxy_bucket_load_balance_enabled toggle
• wire the flag through backend and frontend group management
• update scheduling so sticky routing keeps highest priority first
• after sticky miss, narrow eligible accounts by lower-load proxy_id bucket
• reuse the existing account-level selector after bucket narrowing
• fall back cleanly to the original scheduling path when no proxy-backed candidates exist

Admin account list proxy filter

• support filtering admin account lists by proxy_id
• expose the filter through API and UI
• make large proxy pools easier to inspect without relying on stale cached list results

Verification

• go test ./... -run TestDoesNotExist -count=0
• pnpm typecheck

[Copilot]

Pull request overview

This PR adds account-level OpenAI request override support, introduces optional proxy-bucket load balancing at the group level, and adds proxy-based filtering for the admin account list.

Changes:

• Add per-account OpenAI request override parsing/validation in frontend and apply sanitized overrides in gateway forwarding (excluding top-level model).
• Introduce group flag proxy_bucket_load_balance_enabled and apply proxy-bucket narrowing in schedulers (OpenAI/Gateway/Gemini compat), plus wire it through admin group UI/API and persistence.
• Add proxy_id filtering to admin accounts list across frontend/API/backend, including ETag variation.

Reviewed changes

Copilot reviewed 59 out of 59 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
frontend/src/views/admin/GroupsView.vue	Adds UI toggle to enable/disable proxy-bucket load balancing for groups.
frontend/src/views/admin/AccountsView.vue	Adds proxy_id to filter params and passes proxy list into filters component.
frontend/src/components/admin/account/AccountTableFilters.vue	Implements proxy dropdown filter UI and emits proxy_id updates.
frontend/src/utils/openaiRequestOverrides.ts	Adds JSON parse/stringify helpers with top-level model disallow.
frontend/src/utils/tests/openaiRequestOverrides.spec.ts	Adds unit tests for override parsing rules.
frontend/src/components/account/CreateAccountModal.vue	Adds OpenAI request override textarea and validation on submit.
frontend/src/components/account/EditAccountModal.vue	Adds OpenAI request override textarea and persistence via extra.
frontend/src/components/account/BulkEditAccountModal.vue	Adds bulk edit support for OpenAI request overrides and tests.
frontend/src/components/account/tests/BulkEditAccountModal.spec.ts	Verifies bulk update payload includes openai_request_overrides.
frontend/src/types/index.ts	Wires new fields into TS types for groups and requests.
frontend/src/i18n/locales/en.ts / zh.ts	Adds strings for proxy bucket toggle, proxy filter, and request overrides.
frontend/src/api/admin/accounts.ts	Adds proxy_id to list/listWithEtag query shape.
backend/migrations/081_add_group_proxy_bucket_load_balance.sql	Adds groups.proxy_bucket_load_balance_enabled column.
backend/internal/service/openai_request_overrides*.go	Implements override extraction/sanitization/merge and adds tests + forward tests.
backend/internal/service/openai_gateway_service.go	Applies overrides before extracting request metadata and clears parsed-body cache when modified.
backend/internal/service/openai_gateway_messages.go	Applies overrides for compat path and propagates derived metadata.
backend/internal/service/gateway_service.go	Adds proxy-bucket selection helpers and integrates them into scheduling paths.
backend/internal/service/openai_account_scheduler.go	Applies proxy-bucket narrowing in OpenAI load-balance scheduler.
backend/internal/service/gemini_messages_compat_service.go	Adds concurrency-aware proxy-bucket narrowing in Gemini compat scheduling and updates constructor wiring.
backend/internal/service/*_test.go	Updates repository interface signatures for new proxyID parameter and adds new scheduling tests.
backend/internal/service/admin_service.go + handler/admin/account_handler.go	Adds proxy_id filter support end-to-end and updates ETag inputs.
backend/internal/repository/account_repo.go	Implements proxy filter predicate in query.
backend/internal/repository/group_repo.go + ent/*	Persists and exposes new group flag through Ent schema/runtime/migrations.
backend/cmd/server/wire_gen.go	Wires ConcurrencyService into Gemini compat service constructor.

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