[WAVE 2] Fix multiphase rigid contact force plot mapping

[mickaelbegon]

Summary

• map phase-local rigid contact force rows to the corresponding global plot axes
• preserve the global contact legend across phases
• add a regression test for removing the first contact in a later phase

Root cause

The default BiMapping.to_first values were derived from global contact indices. The rigid-contact function returns a phase-local vector, so a phase containing only the second global contact attempted to read local row 1 instead of row 0. This produced empty or mislabeled plots.

Validation

• MPLCONFIGDIR=/private/tmp/mplconfig-1057 /Users/mickaelbegon/miniconda3/envs/bioptim/bin/python -m pytest tests/shard5/test_configure_problem.py -q
• 7 passed

Closes #1057

---

This change is 

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.86%. Comparing base (89c83a3) to head (f830a96).
⚠️ Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1062      +/-   ##
==========================================
+ Coverage   77.26%   77.86%   +0.60%     
==========================================
  Files         196      196              
  Lines       21506    21503       -3     
==========================================
+ Hits        16616    16743     +127     
+ Misses       4890     4760     -130     

Flag	Coverage Δ
unittests	77.86% <ø> (+0.60%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[mickaelbegon]

Codex analysis

This PR is part of Wave 2 and is rebased onto current master (e8fbc729). It fixes the phase-specific mapping used by rigid contact-force plots and adds focused regression coverage.

Review isolation: it changes only bioptim/dynamics/configure_variables.py and tests/shard5/test_configure_problem.py; it has no source-file overlap with #1065 or #1067.

Validation completed by Codex:

• macOS, Python 3.14 / CasADi 3.7.2: tests/shard5/test_configure_problem.py — 7 passed
• GitHub Actions: 23/23 checks passed
• git diff --check passed

@EveCharbie @pariterre, all local and online checks are green. This PR is ready for review as an independent Wave 2 change.