refactor(core): move session control facts into agent runtime

[limityan]

Summary

• Move provider-neutral session/config/summary facts, session-state labels, dialog-turn id/stats, context-profile policy, and /btw runtime tracking into bitfun-agent-runtime.
• Move the persisted session state sidecar shape and processing-state sanitization out of core persistence; core keeps storage IO, metadata merging, workspace path resolution, and old-path compatibility facades.
• Move the round-level tool confirmation gate into the runtime confirmation owner while core keeps config reads and tool registry lookup.
• Refine the decomposition architecture docs so external systems are modeled as boundary resources, Product Assembly remains the concrete composition root, and non-assembly layers consume stable APIs/ports instead of concrete platform providers.
• Add boundary required rules/self-tests and focused contracts to prevent session/context/confirmation owner rollback.

Compatibility and risk

• No behavior or wire change intended. Session defaults, persisted state JSON shape, session-state serialization/labels, dialog-turn id generation, /btw token semantics, and tool-confirmation skip/permission semantics are covered by tests.
• Existing bitfun-core compatibility paths are preserved, including both bitfun_core::agentic::core::SessionKind and bitfun_core::agentic::core::session::SessionKind.
• bitfun-agent-runtime adds only a contracts-layer dependency on bitfun-core-types for SessionKind; it remains free of bitfun-core, Tauri, product-full, assembly, and concrete manager dependencies.
• The architecture docs now distinguish compile dependency, assembly-time registration, runtime port calls, and external resource calls; external systems are not treated as a repository layer.
• The SDK facade was kept narrow: session config/summary types are owned by the runtime module but are not added to the SDK re-export surface.

Verification

• node --test scripts/check-core-boundaries.test.mjs
• node scripts/check-core-boundaries.mjs
• pnpm run check:repo-hygiene
• cargo test -p bitfun-agent-runtime
• cargo check -p bitfun-core --no-default-features
• cargo check -p bitfun-core --features product-full
• cargo metadata --no-deps --format-version 1
• git diff --check gcwing/main...HEAD
• cargo check --workspace

cargo check --workspace and product-full checks report existing rmcp deprecation warnings in services-integrations/src/mcp/protocol/client_info.rs; no new warnings from this PR were observed.