refactor: move remote disabled surfaces into services

[limityan]

Summary

• Move Remote SSH disabled runtime stubs from bitfun-core into bitfun-services-integrations while preserving the legacy core re-export path.
• Move Remote SSH workspace/session identity construction and disabled remote workspace-search surface to the services owner crate.
• Gate the services-owned disabled remote workspace-search export to lightweight builds only, and update boundary guards plus self-test contracts.
• Add focused service tests and concise plan docs to prevent owner regressions.

Risk and compatibility

• No behavior change intended: disabled SSH/search paths still return explicit unsupported errors.
• Existing bitfun-core public import paths are preserved through compatibility re-exports.
• Lightweight and product-full feature shapes were verified.

Verification

• pnpm run fmt:rs
• pnpm run check:repo-hygiene
• pnpm run build:mobile-web
• node --test scripts/check-core-boundaries.test.mjs
• node scripts/check-core-boundaries.mjs
• cargo metadata --no-deps --format-version 1
• git diff --check
• cargo test -p bitfun-services-integrations --features "remote-ssh workspace-search" --test remote_ssh_contracts
• cargo test -p bitfun-services-integrations --features remote-ssh --test remote_ssh_disabled_contracts
• cargo test -p bitfun-services-integrations --features "remote-ssh workspace-search" --test remote_workspace_search_disabled_contracts
• cargo check -p bitfun-core --no-default-features
• cargo check -p bitfun-core --features product-full
• cargo test -p bitfun-core --lib service::remote_ssh::workspace_state --no-default-features
• cargo test -p bitfun-core --lib service::remote_ssh::workspace_state --features product-full
• cargo check --workspace