feat: complete native Go cutover

[levifig]

Summary

Complete the TypeScript-to-Go cutover for Loaf by removing the legacy TypeScript CLI runtime, moving public command handling to native Go, and packaging native artifacts for supported release targets.

• Replace the TypeScript command surface with Go-native command implementations and tests.
• Add SQLite session state snapshots plus the XDG_DATA_HOME migration path and schema documentation packet.
• Package synchronized native binaries for npm and plugin distribution, with the old dist-cli fallback removed.
• Document the command coverage map and completion audit for the cutover.

Note: linked-worktree .agents/ deletion noise from loaf migrate worktree-storage was intentionally excluded from the branch payload.

Validation

• npm run build:release
• npm test
• go vet ./...
• npm run typecheck
• npm run verify:go-artifacts
• gofmt -l .
• git diff --check
• find cli -type f ( -name ".ts" -o -name ".tsx" ) | sort