fix(tools): repair stale install prefix when ISAACGYM/ISAACSIM_HOME was relocated

[TATP-233]

Summary

• scripts/tools/setup_isaacgym_env.sh and scripts/tools/setup_isaacsim_env.sh claimed to be resumable, but broke after the local cache was moved from the legacy $HOME/.unilab/{isaacgym,isaacsim} to the current ~/.cache/unisim default: conda envs and venvs are not relocatable — entry-point shebangs, activate scripts, .pth/egg-link files, PEP 660 editable finders and conda-meta all hard-code the old prefix. Every skip-check/marker still passed (files exist), but bin/pip could not execute ("required file not found") and the editable isaacgym/isaaclab installs vanished from sys.path, so a re-run died at the pip step instead of resuming.
• Both scripts now detect the stale prefix from the pip shebang and repair it in place (shebang lines only — never binaries; activate scripts; __editable__*_finder.py; .pth/.egg-link; conda-meta), which is far cheaper than re-creating the env / reinstalling multi-GB wheels.
• pip is now invoked as python -m pip instead of the bin/pip entry point, and the isaacgym skip-check also verifies import isaacgym (pip show trusts a stale egg-link); after a repair the isaacsim 06_verify marker is removed so imports are re-verified.
• No user-facing or training-impact behavior: the scripts produce the same runtime layout; they only survive a relocated install root now.

Linked Work

• Issue: n/a (local install breakage found while setting up the isaacgym/isaacsim backends)
• Parent roadmap (when applicable): n/a
• Roadmap declared base (when applicable): n/a
• Milestone: n/a
• Base branch: dev/issue-1042-manager-based-api (both setup scripts only exist on this integration branch; origin/main does not have them yet)

Validation

• make test-all passed on the final local head before this PR was created or updated
• Additional task-specific validation listed below

Commands actually run:

make test-all   # exit 0 (check + test-cov + benchmark entrypoint smoke)
bash scripts/tools/setup_isaacgym_env.sh   # detected relocation, repaired, isaacgym import OK
bash scripts/tools/setup_isaacgym_env.sh   # re-run: all steps skipped, self-check OK
bash scripts/tools/setup_isaacsim_env.sh   # detected relocation, repaired, forced 06_verify re-run passed
bash scripts/tools/setup_isaacsim_env.sh --verify-sim   # all steps skipped; SMOKE TEST OK: Isaac-Cartpole-v0 stepped 20x with 16 envs

Remote CI route:

• not scheduled; local make test-all is the test gate

Impact

• Backend impact: none (install tooling only; isaacgym/isaacsim runtimes unchanged)
• Platform impact: Linux (scripts are Linux-only already)
• Training effect expected: no

Artifacts

• W&B: n/a
• benchmark result: n/a
• video / screenshot: n/a
• ONNX / checkpoint: n/a

Checklist

• Added or updated tests where needed (shell tooling; validated end-to-end on the real relocated cache, no test harness exists for these scripts)
• Updated docs if behavior or workflow changed (script header comments updated; no workflow change)
• Linked the driving issue (none — ad-hoc fix)
• Noted any follow-up work explicitly (none)