fix(studio): restore BytePlus updates and harness performance

[zyn080302]

Summary

• scope thin Studio releases by provider: Volcengine follows the workflow input while BytePlus remains full-only
• keep ordinary veadk studio update bundles lightweight by excluding the full offline Runtime and bundled AgentKit CLI archive while preserving both for first deploy and Release bundles
• prefer the official PyPI artifact host first for BytePlus's pinned compatibility wheels
• keep the Harness main and terminal iframes mounted across tab switches, and reuse a bounded proxy HTTP client instead of creating one client per asset request

Why

The Release workflow previously forwarded one global thin_bundles=true value to both providers. BytePlus accepted the release request but correctly failed during preparation because thin releases are disabled there.

Separately, overseas Studio updates copied the same full offline Runtime into the Scheduler scan Function, Scheduler worker Function, and Studio Function. Returning from the terminal to the Harness main view also unmounted the iframe, which reloaded all client plugins and amplified proxy connections.

Validation

• rebased onto main at 4f3169ca
• affected and new-base Python tests: 203 passed
• provider-scoped workflow structure test: 1 passed
• frontend tests: 1048 passed
• frontend production build: passed
• Ruff check and format on all changed Python files: passed
• full pre-commit (ruff, ruff-format, hardcoded-secret scan): passed
• git diff --check: passed
• Pyright: 37 existing diagnostics in untouched lines of changed files; 0 diagnostics on this PR's added or modified lines
• real lightweight BytePlus package gate: 28.0 s, 6 wheels, 45,169,432-byte ZIP; no wheelhouse/, studio-runtime.json, or AgentKit CLI archive
• the base package appears in the Scheduler scan, Scheduler worker, and Studio Function uploads, so its three-upload payload is about 135,508,296 bytes; this is a lower-bound estimate because Scheduler-specific files and request overhead add a small amount
• BytePlus Harness E2E: three terminal/main switch cycles returned the main view in 251–252 ms; iframe node/document/window/timeOrigin remained unchanged; plugin request delta 0, failed plugin requests 0, loader error false

This PR combines the former provider-scoped Release workflow PR #1076 with the Studio update/Harness performance fix. It does not deploy or publish a Studio release.