feat: prepare KsADK 0.8.3 public candidate

[AgentArcLab]

Status

Draft release candidate. Do not merge or publish yet.

Summary

• export the reviewed Phase 2 plugin, provider, conversation and scheduler foundation
• add the 0.8.3 compatibility matrix, including non-destructive 0.8.2 bundle/runtime fixtures
• include Studio compiled assets while excluding editable Studio frontend sources
• add public documentation, changelog, provenance, package-content and final release-candidate gates

Source binding

• allowlisted source snapshot: 719723f177858e94628c71c1c385b475ed500db3
• export manifest reports a clean source tree
• public source audit: 2,167 paths checked, 0 violations
• targeted public/release tests: 57 passed

Remaining release gates

• publish @kingsoftcloud/ksadk-web@0.3.3 through Trusted Publishing
• resync Studio static assets from that public registry artifact
• rebuild and deploy Hosted UI from the same registry artifact, pinned by image digest
• pass real pre-production multi-turn streaming E2E for a Studio-created Agent and a preserved 0.8.2 historical Agent
• bind final wheel/sdist digests and obtain the recorded release approvals

The changelog intentionally remains Unreleased until these gates pass.