Expand Base contributor standards

[codeforester]

Summary

• Expand STANDARDS.md from Bash-focused rules into a broader Base contributor standard.
• Document the Base layer boundaries across basectl, Bash bootstrap/runtime, Python manifest/project engines, base-wrapper, manifests, testing, docs, and GitHub workflow.
• Add Python CLI conventions using base_cli.App, ctx.log, deterministic JSON, and explicit main(argv) -> int.
• Make the Python CLI launcher standard explicit: public executable shebangs should route through base-wrapper rather than raw Python.
• Add a placement checklist so contributors can decide where new behavior belongs.

Validation

• git diff --check
• LC_ALL=C grep -n '[^ -~]' STANDARDS.md CHANGELOG.md || true\n\nDocs-only change; local runtime tests were not run.\n\nCloses Expand STANDARDS.md for Base architecture and Python CLIs #412