refactor(core): move stable AI DTOs into core types

[limityan]

Summary

• Move stable AI config, message, tool-call, and connection-test DTOs into bitfun-core-types.
• Preserve legacy bitfun-ai-adapters::types and bitfun-core::util::types compatibility exports.
• Gate concrete AI adapter runtime, CLI credential acquisition, debug ingest, workspace search, and direct HTTP server/client dependencies behind explicit core features.
• Extend core-boundary rules and self-tests so no-default core stays free of concrete AI/HTTP/workspace-search owners, contracts do not encode provider endpoint behavior, and product-domain facade feature dependencies stay complete.

Risk and impact

• No provider request/stream behavior is intentionally changed; adapter tests cover request URL compatibility and stream behavior.
• GeminiUsage and GeminiResponse remain adapter-owned because they depend on stream usage conversion details.
• bitfun-core --no-default-features keeps remote SSH workspace identity as a compatibility dependency; this PR only trims the concrete AI/runtime/debug/search owners documented in the plan.

Verification

• pnpm run fmt:rs
• node --test scripts\check-core-boundaries.test.mjs
• node scripts\check-core-boundaries.mjs
• cargo test -p bitfun-core-types
• cargo test -p bitfun-ai-adapters
• cargo check -p bitfun-core --no-default-features
• cargo check -p bitfun-core --no-default-features --features product-full
• cargo check -p bitfun-core --no-default-features --features product-domains
• cargo check -p bitfun-cli
• cargo check -p bitfun-acp
• cargo check -p bitfun-desktop
• pnpm run check:repo-hygiene
• cargo metadata --no-deps --format-version 1
• git diff --check
• cargo tree -p bitfun-core --no-default-features --depth 1 | Select-String -Pattern 'bitfun-ai-adapters|reqwest|axum|tower-http|workspace-search|remote-ssh-concrete'