fix(studio): harden Skill detail loading

[evanlowe]

Summary

• make Skill detail loading region-aware for legacy SkillSpace archives
• fall back from GetSkillVersion to GetSkillInfo only for the legacy interface-type mismatch
• preserve sanitized upstream exception details in Studio API errors
• ignore macOS ZIP metadata and skip binary assets in text previews while keeping materialization strict
• keep the Skill file browser usable on narrow/mobile viewports
• include rebuilt Studio web assets

Verification

• uv run pytest tests/cli/test_frontend_skill_spaces.py tests/cli/test_generated_agent_backend_codegen_extended.py tests/frontend/test_skills_server.py tests/skills/test_adk_skill_materializer.py tests/test_ve_tos.py -q (131 passed)
• cd frontend && npm test (761 passed)
• cd frontend && npm run build
• uv run pre-commit run
• uvx pyright --pythonpath .venv/bin/python frontend/server/skills/repository.py frontend/server/skills/routes.py frontend/server/skills/service.py veadk/cli/generated_agent_skills.py veadk/skills/materializer.py (0 errors)

Manual coverage

• verified Beijing legacy SkillSpace Skills, including cloud-migration-qa and a ZIP containing __MACOSX/._SKILL.md
• verified Shanghai SkillSpace details and managed Skills containing binary font assets
• reviewed Skill detail layout at desktop and 390x844 viewports

Known limitation

• broader touched-file Pyright checks still report existing type issues in veadk/cli/cli_frontend.py and veadk/integrations/ve_tos/ve_tos.py; this change does not add errors in the isolated modules above