[Workflow] Report when playback agents are running (#7560)

# Description

Adds a terminal status message after playback initialization completes
so users know the process is actively running and how to stop it.

The message is customized for:

- trained policy playback across RL-Games, RSL-RL, Stable-Baselines3,
skrl, and RLinf
- the zero agent
- the random agent

## Type of change

- New feature (non-breaking change which adds functionality)

## Release backport

- [x] <!-- backport-active-release --> Backport this pull request to the
active release branch after it merges into `develop`

## Screenshots

Not applicable; this change affects terminal output only.

## Validation

- `uv run python -m pytest source/isaaclab_rl/test/test_entrypoints.py`
(32 passed)
- `SKIP=check-changelog-fragments uv run isaaclab -f` (all applicable
formatting and lint checks passed)
- Changelog validation against upstream `develop` (passed)

## Checklist

- [x] I have read and understood the contribution guidelines
- [x] I have run the pre-commit formatting and lint checks
- [x] Documentation changes are not required for this terminal-only
behavior
- [x] My changes generate no new warnings
- [x] No new test is needed for static terminal text; the existing
entrypoint suite passes
- [x] I have added a changelog fragment for `isaaclab_rl`
- [x] My name already exists in `CONTRIBUTORS.md`

(cherry picked from commit 6b8e133)

Author: StafaH

source/isaaclab_rl/changelog.d/add-playback-ready-messages.rst

@@ -0,0 +1,5 @@
+Added
+^^^^^
+
+* Added mode-specific terminal messages when policy playback, the zero-action agent, or the random-action agent
+  finished initialization.

source/isaaclab_rl/isaaclab_rl/entrypoints/backends/play_rl_games.py

@@ -199,6 +199,7 @@ def main():
             _ = agent.get_batch_size(obs, 1)
             if agent.is_rnn:
                 agent.init_rnn()
+            print("[INFO] Policy playback is running, press Ctrl+C to exit...")
             try:
                 while True:
                     start_time = time.time()

source/isaaclab_rl/isaaclab_rl/entrypoints/backends/play_rlinf.py

@@ -161,6 +161,7 @@ def main():
     )
 
     runner.init_workers()
+    print("[INFO] Policy playback is running, press Ctrl+C to exit...")
     runner.run()
 
 

source/isaaclab_rl/isaaclab_rl/entrypoints/backends/play_rsl_rl.py

@@ -218,6 +218,7 @@ def main(env_cfg: ManagerBasedRLEnvCfg | DirectRLEnvCfg | DirectMARLEnvCfg, agen
             screen.close()
             obs = env.get_observations()
             timestep = 0
+            print("[INFO] Policy playback is running, press Ctrl+C to exit...")
             try:
                 while True:
                     start_time = time.time()

source/isaaclab_rl/isaaclab_rl/entrypoints/backends/play_sb3.py

@@ -187,6 +187,7 @@ def main():
             screen.close()
             obs = env.reset()
             timestep = 0
+            print("[INFO] Policy playback is running, press Ctrl+C to exit...")
             try:
                 while True:
                     start_time = time.time()

source/isaaclab_rl/isaaclab_rl/entrypoints/backends/play_skrl.py

@@ -242,6 +242,7 @@ def _main():
             obs, _ = env.reset()
             states = env.state()
             timestep = 0
+            print("[INFO] Policy playback is running, press Ctrl+C to exit...")
             try:
                 while True:
                     start_time = time.time()

source/isaaclab_rl/isaaclab_rl/entrypoints/simple_agents.py

@@ -85,6 +85,10 @@ def run(argv: list[str] | None = None, *, policy: PolicyName) -> None:
         # reset environment
         env.reset()
         zero_action_policy = _create_zero_action_policy(env) if policy == "zero" else None
+        if policy == "zero":
+            print("[INFO] Zero agent is running, press Ctrl+C to exit...")
+        else:
+            print("[INFO] Random agent is running, press Ctrl+C to exit...")
         # simulate environment
         # keep running while any visualizer is open, and until the step budget is exhausted
         sim = env.unwrapped.sim