refactor(runtime): close tool and product-domain owner slices

[limityan]

Summary

• Move provider-neutral tool execution presentation helpers into bitfun-agent-tools, covering structured result fallback text, error argument preview, steering-interrupted presentation, and invalid tool-call error messages.
• Complete the low-risk HR-B product-domain owner slice by moving MiniApp import metadata stamping and import runtime-state persistence into bitfun-product-domains helpers/facade.
• Keep runtime execution ownership in core: ToolUseContext, tool state transitions, MiniApp filesystem/source IO, compiler orchestration, worker process, host dispatch, built-in asset seeding/marker IO, function-agent Git/AI adapters, provider acquisition, and AI transport error mapping remain unchanged.
• Extend owner-crate contract tests, focused core regression coverage, boundary/self-test anchors, and concise docs/AGENTS guidance for the updated HR-A/HR-B boundary.

Verification

• cargo test -p bitfun-agent-tools
• cargo test -p bitfun-core agentic::tools::pipeline::tool_pipeline::tests -- --nocapture
• cargo test -p bitfun-product-domains --no-default-features
• cargo test -p bitfun-product-domains --features miniapp
• cargo test -p bitfun-product-domains --features product-full
• cargo test -p bitfun-core miniapp -- --nocapture
• cargo test -p bitfun-core function_agents -- --nocapture
• cargo check -p bitfun-core --features product-full
• node scripts\check-core-boundaries.mjs
• $env:BITFUN_BOUNDARY_CHECK_SELF_TEST='1'; node scripts\check-core-boundaries.mjs
• git diff --check

Risk review

• Behavior is intended to be equivalent: tests lock existing tool JSON/text shapes, argument truncation markers, MiniApp import fallback/runtime state, and function-agent Git/AI adapter boundaries.
• The PR does not move concrete IO/process/Git/AI execution into owner crates and does not change product feature gates or release-shape wiring.
• Existing untracked local files are not included in this PR.