docs(linux): refresh ROADMAP against shipped Phase 2/3 work

[cozyGarage]

Summary

• Reconcile linux/ROADMAP.md with what the tree already ships (four drivers, full Value set, workspace tabs, Structure/DDL, filters, SSH, read-only mode, query history, connection monitor, gettext scaffolding, CI integration jobs).
• Update linux/README.md status line and stack table so newcomers are not told scaffolding "has not started yet".
• Document Podman as a Docker-compatible backend for testcontainers in docs/testing.md.
• Add local contributor helpers: scripts/ci-local.sh, scripts/smoke-postgres.sh, scripts/dev-env.sh, and a smoke_local Postgres test that hits an already-running instance.

Test plan

• Read ROADMAP against crates/ inventory (drivers, services, UI modules)
• cargo test -p tablepro-driver-postgres --test smoke_local against local Podman Postgres on :54329
• cargo test --test integration -p tablepro-driver-postgres -- --include-ignored --test-threads=1 via DOCKER_HOST=unix:///run/user/\$UID/podman/podman.sock
• Same for MySQL integration suite
• CI Build Linux workflow green on this branch

Made with Cursor

[cozyGarage]

I have read the CLA Document and I hereby sign the CLA.