Make project replacement idempotent

[codeforester]

Summary

• Treat --replace-project on an already-standard GitHub Project as a non-fatal INFO no-op instead of an error.
• Continue the normal Project configure path afterward so link/backfill/default repair remains idempotent.
• Update Base docs and .ai-context/ to clarify that already-standard Projects are left intact.

Issue

Fixes #901

Validation

• PYTHONPATH=lib/python:cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pytest cli/python/base_github_projects/tests/test_project_configure_replacement.py - 5 passed
• PYTHONPATH=lib/python:cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pytest cli/python/base_github_projects/tests - 30 passed
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats cli/bash/commands/basectl/tests/gh.bats - 33 passed
• git diff --check
• env -u BASE_HOME BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash ./bin/base-test - 503 passed, 1 skipped; 430 BATS passed

Demo Impact

None.

Notes

The updated replacement regression test failed before the implementation with ProjectError: Project 'base-demo' already has standard Base views; refusing to replace it.

Checklist

• Branch name follows <category>/<issue>-<YYYYMMDD>-<slug>.
• PR is scoped to one issue, unless a documented multi-issue exception applies.
• PR body explains what changed and how it was validated.
• Validation commands were run from the current checkout or worktree, or unavailable checks are explained.
• Relevant BATS and Python tests pass.
• Bug fixes include regression proof or a documented reproduction when practical.
• Documentation is updated when behavior or user-facing commands change.
• AI context is updated in .ai-context/, or the PR body explains why it is not applicable.
• PR includes Fixes #<issue> or Closes #<issue> when it should close the issue.
• Demo Impact is meaningful for needs-demo work, or explicitly says None.