Task: Persist provider settings in PostgreSQL

Identity

Replace production file persistence for the four provider setting groups (Volcengine visual, EvoLink, Seedance, and Bailian) plus image/video engine assignments with PostgreSQL-backed runtime settings.
Keep environment variables as fallback values and leave authentication, database, billing, and OSS deployment configuration outside this migration.
Make provider submission, job construction, capability reporting, and health reporting observe successful setting changes without a process restart.
Change the settings UI to submit only edited fields and accurately report that a successful save is immediately effective.
Add migration and regression coverage for persistence, precedence, secret preservation, and runtime consumption.

Preserve the accepted static Web plus Go-only API architecture and the existing super-administrator authorization boundary on /api/settings.
PostgreSQL is the production source of truth; saved database values override environment fallback values, while unset values continue to use environment configuration and existing defaults.
Store values in plaintext for this first functional delivery, as explicitly requested; encryption and secret rotation remain follow-up hardening.
Do not modify the pre-existing untracked .idea/ directory.
The repository-required task_context.py coordination helper is not present in this checkout, and .git is read-only in this environment, so this task records ownership here and works in the user-authorized current worktree without creating a feature branch.
Feature work updates only this task-scoped record; canonical architecture and decision documents remain integration-owned.

Added migration 0003_platform_runtime_settings.sql and explicit application-role/readiness coverage for the new PostgreSQL table. Provider settings are upserted transactionally with a revision and update timestamp.
The production settings service now persists the four provider groups plus image/video engine assignments in PostgreSQL. Database rows override environment and legacy file fallback values; blank secret submissions still preserve the existing value and secret values remain blank in API payloads.
Provider configuration is refreshed at both runtime seams: quote/job construction resolves current engine/model/defaults, and Worker submit/query resolves a fresh adapter with the current credential and Base URL. Capability and health projections also observe the mutable provider state.
Removed the production startup credential gate and obsolete bootstrap flag. The API can start before providers are configured, while a request selecting an unconfigured provider still fails with 503 and never falls back to Mock.
The settings client tracks dirty keys and posts only edited values, preventing a provider save from also attempting writes for unrelated file-backed groups. Successful provider saves report immediate application without a restart.
Provider Secret injection is now an optional environment fallback in ACK; deployment guidance documents migration 0003, database precedence, and the no-restart behavior. Values are intentionally plaintext for this delivery.

RED: npx vitest run tests/settings-go-contract.test.ts failed because the compatibility fixture still required restart and migration 0003 did not yet exist.
PASS: official Go 1.26.6 archive checksum matched the published SHA-256; the toolchain was extracted only under /private/tmp and removed after verification.
PASS: gofmt -l backend returned no files.
PASS: go test ./... across all Go packages.
PASS: go vet ./....
PASS: go build -o /private/tmp/nianaigc-zhinian-api ./cmd/zhinian-api.
PASS: affected Go package regression rerun for postgres, settings, application, jobs, and httpapi after final transaction cleanup.
PASS: npm test (55 files, 176 tests).
PASS: npx tsc --noEmit --incremental false.
PASS: npm run build (all routes statically exported).
PASS: npm run deploy:check (7 ACK manifest files).
PASS: git diff --check.
The repository-referenced check_project_docs.py, check_doc_drift.py, and task_context.py helpers are not present in this checkout, so those specific project-document/coordination commands could not be run.

Consider encrypting provider secrets at rest and recording secret-access audit metadata after functional persistence is deployed and verified.
Before rolling out the new Go image, execute migration 0003 and re-provision application-role grants, then smoke save each provider group and submit one real request through every configured engine against the target RDS/ACK environment. No live database or cluster mutation was performed in this task.

Record PostgreSQL-backed mutable provider settings and the database-over-env precedence rule in canonical architecture during integration.