feat(remote-ssh): complete multi-hop and container workspaces

[bobleer]

Summary

Closes #1725.

• introduce a transport-neutral workspace stdio abstraction shared by SSH and Docker-backed workspaces, including stdin/stdout/stderr, completion, interruption, cancellation, ACP, terminal, command, agent, and search paths
• complete arbitrary ProxyJump chains, per-hop SSH config identities, ssh-agent/certificate/keyboard-interactive authentication, bounded retries/timeouts, and staged connection diagnostics
• support local and remote Docker container discovery, Auto sshd probing with Docker Exec fallback, TTY/non-TTY execution, and binary-safe atomic file transfers with cancellation
• add one unified connection entry point in the UI, container selection, all authentication modes, effective-access reporting, and localized staged test results
• preserve existing saved connections, workspaces, legacy agent profiles, password-vault behavior, and reconnect semantics across upgrades
• harden macOS/Windows/Linux client behavior: preserve split UTF-8 across independent stdout/stderr streams, keep remote paths POSIX, reject unsafe local filename mappings and symlink traversal, and signal Docker process groups inside the container before closing the Docker CLI
• document the architecture, capability matrix, compatibility guarantees, and security boundary

Compatibility

Existing serialized connection/workspace records remain loadable through serde defaults and legacy auth deserialization. Startup does not prune an existing workspace when its connection needs credentials or is temporarily unavailable. Auto is re-probed on reconnect, while the original saved configuration is retained.

Normal existing mirror/session path mappings are unchanged. Safe legacy dot-segment paths keep resolving to their previous effective mirror directories, while paths that would escape the mirror root are contained. Previously unsafe or unrepresentable recursive-transfer entries now fail explicitly instead of being silently skipped, overwritten, followed outside the selected tree, or mapped through host-specific path semantics.

Legacy local-Docker profiles with an empty password placeholder continue to load and connect without a password-vault entry. Docker process supervision also degrades to the previous transport-level cancellation behavior when a read-only container filesystem cannot create its optional PID tracking file, so supervision does not become a new runtime prerequisite after upgrade.

Verification

• cargo check --workspace
• cargo check -p bitfun-desktop
• cargo test -p bitfun-services-integrations --features remote-ssh,remote-ssh-concrete,workspace-search remote_ssh
• cargo test -p bitfun-services-integrations --features remote-ssh-concrete remote_ssh --lib
• cargo test -p bitfun-services-integrations --features remote-ssh,remote-ssh-concrete,workspace-search --test remote_ssh_contracts
• cargo test -p bitfun-services-integrations --features remote-ssh-concrete --test remote_ssh_contracts
• cargo test -p bitfun-services-integrations --features remote-ssh --test remote_ssh_disabled_contracts
• cargo test -p bitfun-desktop remote_workspace_policy --lib
• cargo test -p bitfun-desktop api::ssh_api::tests --lib
• real Docker round-trip integration (binary files, stdio/stderr/exit, cancellation preserving the prior destination)
• node --test scripts/check-core-boundaries.test.mjs
• pnpm run type-check:web
• pnpm run lint:web
• pnpm --dir src/web-ui run test:run src/features/ssh-remote/SSHRemoteProvider.test.tsx src/features/ssh-remote/remoteWorkspaceReconnect.test.ts
• pnpm run i18n:audit
• pnpm run theme:color-audit:all
• pnpm run check:repo-hygiene
• pnpm run check:github-config