feat: add Managed Agents runtime and portable sandbox integration

[mofanke]

Managed Agents workers can now run through the published Anthropic SDK without the adjacent customized SDK wheel. The runtime handles environment/account Work polling, leases, scoped authentication, cancellation, event replay and completion; Example 16 delegates to the packaged implementation.

• Add reusable Session/Skill/MCP resource integration, pinned Skill materialization, Session Identity handling and opt-in configured model credentials for local non-AgentKit execution.
• Carry the non-UI Ark context/cache/tool-call updates, API-key provider selection and opt-in Feishu streaming while preserving upstream lifecycle behavior.
• Add a portable locked Worker image, SDK integrity check, launch/deployment examples, contract tests and bilingual designs/specifications. Official tool configuration type discriminators work alongside legacy names. SDK versions remain locked; no frontend code is changed.

Validation:

• After fetching/rebasing the latest official main: all-file pre-commit passed; all changed unit-test modules passed (262 + 71 tests).
• Earlier scoped parallel regression: 6963 passed, 42 skipped, 4 xfailed, 6 subtests passed. Seven existing UI failures were reproduced on untouched official main and explicitly deselected; the unfiltered default regression gate is therefore not reported as passing.
• Python 3.10 official-SDK adapter/credential subsets passed. Worker image installs official Anthropic 1.3.0, with 1389 Python files matching wheel RECORD and installation verified by locked artifact hashes.
• Real Kubernetes acceptance with independently installed official Anthropic SDK 1.5.0 passed two model turns, bash/read/write/edit/glob/grep, frozen Skill instructions and continuation after replacing the Worker. Both model Work items stopped; test Session/Agent/Skill cleanup passed. Final deployed source hashes match this implementation.

Acceptance covers configured Ark credentials and local tools through the internal service. Public APIG authentication, cloud Runtime Identity issuance and automatic remote tool dispatch remain outside this acceptance. Version-sensitive official SDK extraction/context-manager helpers are documented and tested; SDK source is not overridden.