feat: add Volcengine Ark Coding Plan (China)

[Astro-Han]

Summary

• Add Volcengine Ark Coding Plan (China) as the independent persisted provider volcengine-coding-plan, with its dedicated API-key endpoint and official fallback model allowlist.
• Carry the access path through Core, Runtime, CLI, Storage, Headless policy, and Desktop catalog/detail surfaces, including deterministic reasoning plus two-stage tool-call coverage.
• Reuse the single byte-identical Volcengine SVG, asset-mask route, and third-party notice introduced by feat: add Volcengine Ark China direct API #909; no parallel brand asset or notice seam is added.

Why

Volcengine documents Ark Coding Plan as a subscription for interactive AI coding tools, with its own OpenAI-compatible endpoint (https://ark.cn-beijing.volces.com/api/coding/v3) and Ark-console API key. It is not the Ark direct API, Ark Agent Plan, or BytePlus ModelArk access path. The public personal Plan API does not document a /models contract; the published ListArkCodingPlanModel operation uses IAM/HMAC authentication instead of the Plan API key, so this integration deliberately uses the documented static model list and disables model refresh.

Official contract references: plan overview, quick start, FAQ and usage boundary, subscription terms, and ListArkCodingPlanModel.

Refs #860.

Scope

• No Phase 7 work.
• No Ark direct, Ark Agent Plan, or BytePlus ModelArk behavior is changed or aliased.
• Headless environment credential loading remains unavailable because the public Plan terms limit the subscription to supported AI coding tools; deterministic runtime tests use only synthetic local responses.
• No live provider smoke was run because no safe user credential was available. No secret or raw provider response was recorded.

Verification

• npm test — passed before the final upstream rebase with zero failures across all workspaces.
• npm run typecheck — passed on final SHA after rebasing build(cu): pin cua-driver artifact integrity #894.
• node ../../worktree-bootstrap.mjs — passed on final SHA, including complete workspace build, Desktop renderer build, public notice check, and stale-dist check.
• Provider/credential/persistence/runtime/headless/Desktop governance and feat(cu): wire verified backend into desktop #895 Desktop Computer Use contracts — 211/211 passed on final SHA, including the exact glm-5.2 reasoning and two-stage tool-call wire loop.
• node --test scripts/cua-driver-provenance.test.mjs — 4/4 passed, preserving build(cu): pin cua-driver artifact integrity #894 artifact-integrity coverage.
• Targeted local Electron provider journey — 1/1 passed for Coding Plan catalog, endpoint, persisted ID, default model, API-key field, disabled refresh, detail page, and shared mask rendering. CI E2E remains the release gate.
• Vendored Volcengine SVG compared byte-for-byte with lobehub/lobe-icons commit e4302041fbb3039608d25f9f618bd462783b875e, path packages/static-svg/icons/volcengine.svg; both SHA-256 values are f29d0bdc284b33d8664ef221add7fbf06a5b370ef92767fa33f6020c914d3d33.
• git diff --check origin/main...HEAD — passed; the branch does not modify the SVG or THIRD_PARTY_LICENSES.txt.

No screenshot is attached because this uses the existing registry-driven catalog/detail layout and the existing governed Volcengine mark without introducing new pixels or interaction design. The deterministic Electron journey and asset-mask governance contract are the direct UI evidence.

Impact

Users in China can configure Ark Coding Plan independently from Ark direct API access. Existing persisted providers and credentials are unchanged; there is no migration. The new provider stores its own ID, endpoint, API key, and exact model selection through the existing connection seams.

Reviewer notes

The main review boundary is access-path separation: /api/coding/v3 plus fallback-only discovery and no headless env credential mapping must remain distinct from #909's /api/v3 direct provider. Rollback is the four commits in this branch; the shared Volcengine asset remains owned by #909.

Ready for review

• Verification is complete and the results above are current
• Impact, compatibility, migration, documentation, and release-note needs are addressed
• User-visible UI/UX changes include visual evidence, or Verification explains why it is not applicable