feat(account): wire admin OAuth onboarding

[ijry]

Changes

• Add admin account OAuth start/callback endpoints and route wiring.
• Enable the admin account add dialog OAuth tab to open onboarding popup and refresh on completion.
• Fix golangci-lint findings by explicitly ignoring deferred close errors.
• Return inviter lookup DB errors from invite rebate instead of swallowing them.
• Stabilize dockertest DB readiness by closing failed retry connections and increasing MySQL wait time.

Motivation

• Completes account-pool OAuth admin onboarding follow-up so admins can initiate OAuth pulls from the UI.
• Keeps CI green after PR feat: M2 收尾 — 适配器补全 / 修复死路由 / 账号池 OAuth PKCE 核心 #1 was merged and the branch received follow-up commits.

Testing

• go run github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.2 run
• PROAPI_MASTER_KEY=0123456789abcdef0123456789abcdef go test -race -count=1 ./...
• PROAPI_MASTER_KEY=0123456789abcdef0123456789abcdef go test -race -count=1 -tags=integration ./...
• PROAPI_MASTER_KEY=0123456789abcdef0123456789abcdef go build -tags embed -ldflags="-s -w" -o bin/proapi ./cmd/proapi
• pnpm -C web typecheck
• pnpm -C web/admin build
• pnpm -C web/user build
• pnpm -C docs-site install --frozen-lockfile && pnpm -C docs-site build
• git diff --check

Breaking Change

None.