refactor(runtime): route CLI interaction responses through SDK

[limityan]

Summary

• Add typed Agent Runtime SDK contracts for tool confirmation, rejection, and user-answer responses.
• Route CLI/TUI/Exec interaction responses and Peer Host confirmation/rejection through the SDK while retaining Core ToolPipeline and user-input ownership.
• Remove only the replaced compatibility-facade methods and centralize user-facing RuntimeError message conversion.
• Fix issues found while re-reviewing the previous PR: restore/transcript errors no longer leak internal error-kind prefixes, capability documentation now matches each product surface, and typed user-input errors preserve the existing Desktop string contract.

Scope boundaries

• No approval-policy or runtime-owner migration.
• No new Peer Host user-answer command.
• No Desktop, ACP, remote-control, or HarmonyOS runtime adoption in this PR.
• The Core compatibility facade remains for fixed-ID session creation, model updates, branching, usage, snapshots, and persistence maintenance.

Validation

• rustup run nightly cargo check --workspace
• rustup run nightly cargo test -p bitfun-agent-runtime
• rustup run nightly cargo test -p bitfun-cli
• Targeted Core interaction-response and previous-PR error-compatibility tests
• rustup run nightly cargo fmt --all -- --check
• Core boundary check and its 15 self-tests
• Repository hygiene check

The installed stable Rust toolchain is locally inconsistent, so Rust validation was run with the installed nightly toolchain. The workspace check completed successfully; only existing MCP deprecation warnings remain.