feat(RL): PPO pipeline with GRU body-state embeddings for Reacher-v5 with 256 size

[PushpitaJoardar]

Summary

Implemented the RL pipeline(RNN estimation) for Reacher-v5, supporting both
raw observation baseline and GRU-embedded observation conditions as
described in the Body-State Manifold Learning proposal.

Changes

New Files

• articulated/rl/environment.py — ReacherWithEmbedding wrapper (raw + embedded modes)
• articulated/rl/agent.py — RLAgent with PPO, VecNormalize, all config fields
• articulated/rl/train.py — Training script with eval and TensorBoard logging
• articulated/rl/fit_pca.py — PCA fitting script for GRU embedding compression
• articulated/configs/rl/baseline.yaml — Raw obs baseline (500K steps)
• articulated/configs/rl/baseline_tuned.yaml — Tuned baseline (1M steps)
• articulated/configs/rl/baseline_tuned2.yaml — Tuned baseline, lower LR
• articulated/configs/rl/embedded.yaml — GRU-embedded obs config
• articulated/configs/estimation/gru_so2.yaml — GRU estimation config (SO2)

Modified Files

• articulated/shared/robot_arm.py — Added RobotArm2DKinematics for SO(2)
• articulated/estimation/datamodule.py — SO(2) manifold support
• articulated/estimation/model.py — GRU support + get_embedding() interface
• articulated/estimation/train.py — Training script updates

Results

Condition	Mean Reward	Timesteps
Baseline PPO (raw obs)	-3.80	500K
Embedded RNN (val/acc=24%)	-9.67	1M
Embedded GRU (val/acc=99%)	-6.19	1M

Notes

• GRU with kappa=20, seq_length=50 achieves val/acc=0.993
• Embedded obs = [h_t | cos/sin joints | target_pos | fingertip_vec]