feat: dual-framework support (IsaacLab + mjlab)

[fan-ziqi]

Summary

Adds dual-backend support: every existing IsaacLab task continues to work, and the project gains a parallel mjlab path through a new adapter layer at robot_lab.framework. Backend is selected at runtime via --framework {isaaclab,mjlab} to a top-level dispatcher; users provision per-framework venvs via ./setup_env.sh.

What's in this PR

3 commits:

1. feat: dual-framework adapter layer + venv automation

   • robot_lab.framework package: cfg-type aliases, MDP function aliases, sensor / event / scene / contact factories, RL cfg shim, app launcher, register_task, manager_container, make_observation_group — all with parallel implementations on both backends.
   • assets/builders/{isaaclab,mjlab}.py + assets/data/<robot>.py for framework-neutral robot data + per-backend cfg construction.
   • setup_env.sh: provisions .venvs/{isaaclab,mjlab} with fixed Python versions; idempotent. The IsaacLab side drops a .pth so the wheel-bundled isaaclab_rl/_tasks/_assets subpackages become importable without a separate git clone IsaacLab.
   • pyproject.toml: PEP 621 metadata + mutually exclusive [isaaclab] / [mjlab] extras (no [all]: IsaacSim forces py3.11, mjlab is native to py3.12).

2. refactor: migrate business code to robot_lab.framework adapter

   • robot_lab/__init__.py + tasks/__init__.py: defensive try/ImportError so import robot_lab works under both venvs, even pre-SimApp.
   • assets/<vendor>.py (10 files): wrap IL-only top-level cfg constants in try/ImportError so the modules import cleanly under mjlab.
   • assets/unitree.py::build_unitree_a1_cfg(): factory dispatching on get_framework().
   • velocity_env_cfg.py + mdp/{rewards,events,observations,commands}.py: imports come from robot_lab.framework. Math helpers fall back to mjlab's lab_api. Type-only imports moved into TYPE_CHECKING blocks.
   • 24 velocity task __init__.py files + beyondmimic G1: switched from gym.register to robot_lab.framework.register_task. Task IDs unified to RobotLab-Velocity-...-v0 (Isaac- infix dropped). Every task is framework_required="isaaclab" for now: existing env_cfg subclasses inherit IL-style nested @configclass and don't survive class-body evaluation under mjlab. Authoring mjlab-native env cfgs is a follow-up beyond this PR.

3. feat: scripts dispatcher + framework tests + docs

   • scripts/{train,play}.py: top-level dispatcher with auto-exec into the right venv.
   • scripts/isaaclab/...: existing scripts moved here. Log root unified to logs/isaaclab/<exp>/<run> (was logs/{rsl_rl,skrl,cusrl}/).
   • scripts/mjlab/reinforcement_learning/rsl_rl/{train,play}.py: thin wrappers over mjlab.scripts.{train,play}. mjlab CLI stays tyro-native (--env.scene.num-envs ...).
   • tests/framework/: detect / spec / container / subprocess-isolated imports / AST-based no-direct-imports audit.
   • docs/migration-from-subclass.md: walks IL users through the small set of changes.
   • README.md: new "Frameworks" section + mjlab column in Version Dependency.

Migration impact for existing IsaacLab users

Two breaking changes:

1. Task IDs lose the Isaac- infix: RobotLab-Isaac-Velocity-Rough-Unitree-A1-v0 → RobotLab-Velocity-Rough-Unitree-A1-v0. Update shell aliases / CI / wandb run names.
2. Log root moves from logs/{rsl_rl,skrl,cusrl}/<exp> → logs/isaaclab/<exp>. Old run links no longer resolve; new runs work normally.

Custom env_cfg subclasses, __post_init__ overrides, and agent cfgs all keep working unchanged. See docs/migration-from-subclass.md for details.

Verification

• pytest tests/framework/ — 23/23 pass under .venvs/mjlab (subprocess-isolated import smoke + AST audit + container/detect/spec unit tests).
• pytest tests/framework/test_no_framework_imports.py — 40 files scanned, 0 violations of the "business code does not import isaaclab/mjlab directly" invariant.
• pytest -m smoke tests/integration/ — mjlab list-tasks pass; IL side currently skipped on this dev host pending an external IsaacSim 5.1 + Python 3.11 SimApp bootstrap fix (verified to be external — a fresh venv with the same code triggers the same kit-bootstrap error).
• Both venvs cleanly import robot_lab, import robot_lab.framework, and import robot_lab.tasks.
• All 24 velocity tasks register on IsaacLab (Isaac- infix dropped); under mjlab they are silently skipped with INFO[robot_lab.framework] task ... requires framework='isaaclab'; skipping under current framework. log lines.

Out of scope (follow-ups)

• Authoring at least one mjlab-native env_cfg factory function (Unitree A1 is the natural template — its asset builder is already in place).
• Porting the 100+ wheel-bundled IsaacLab subpackage paths to a more robust resolution (current .pth approach works but is wheel-internal).

Why some things look the way they do

• framework_required="isaaclab" on every task is intentional, not laziness. mjlab's ObservationGroupCfg requires a terms= argument that IsaacLab's doesn't take. The existing nested-@configclass LocomotionVelocityRoughEnvCfg cannot evaluate under mjlab. The skip-with-info pattern is the cleanest way to keep IL behavior identical while leaving the door open for mjlab-native cfgs.
• configclass is intentionally NOT exposed by robot_lab.framework. It's a dataclass-like decorator on IsaacLab and a no-op identity on mjlab; exposing it would be a footgun (silent semantic divergence). Internal code uses from isaaclab.utils import configclass directly.
• The [all] extra was deliberately omitted. IsaacSim forces Python 3.11; mjlab is native to 3.12. Combining them in one venv requires picking 3.11 and degrading mjlab. Two-venv discipline is the project's design choice.

[fan-ziqi]

Closing — the implementation took the wrong shape. Reopening fresh with a proper IL-named framework layer instead of try/except scaffolding around isaaclab imports. See follow-up PR.