feat(agent-sdk): migrate to 0.3.270

[srothgan]

Summary

• Upgrade both Agent SDK package surfaces and the bridge runtime version guard to 0.3.270.
• Honor the SDK's permission safety hints: default the permission prompt to the deny option when the SDK asks for it, and suppress the "Always allow" rule when the SDK marks a request as session-only.
• Let the SDK control Task and Todo tool availability instead of assuming they exist.
• Preserve plural user-message correlation, result-level permission denials, the new verification_required and cloud_credential_error retry classes, and the rate-limit limit_scope field end to end.
• Hold session plugin reloads that would invalidate the prompt cache, surface the sanitized cache impact in a confirmation overlay, and only force the reload on explicit confirmation.
• Render staged Write output, project memory list and read results, and the expanded Artifact publish and asset ownership metadata.

Why

Agent SDK 0.3.270 changes several host-facing contracts. Permission requests now carry safety hints the host must respect to avoid presenting unsafe defaults, plugin reloads can be held to protect the prompt cache, and tool results carry new metadata that would otherwise render as opaque JSON. Tracking the release keeps the bridge version guard, the wire types, and the TUI rendering in step with the bundled Claude Code behavior.

Closes #372

Validation

• Automated: cargo fmt --all -- --check, cargo clippy --all-targets --all-features -- -D warnings, cargo test (1820 lib tests), npm --prefix agent-sdk test (392 tests), npm --prefix agent-sdk run lint, npm --prefix agent-sdk run knip, npm --prefix agent-sdk run audit.
• Manual: Not exercised interactively.
• Screenshot/video (if UI changed): N/A

Notes

• Breaking changes: None expected. Existing permission flows keep their previous defaults unless the SDK sends the new hints.
• Docs updated: CHANGELOG.md gains Unreleased entries for this PR and fix(input): clear SDK prompt suggestion only after a prompt is dispatched #377.
• Governance/release impact: Ships the Agent SDK and bundled Claude Code parity update together with the host features it enables.