Add verified Windows and Linux x86-64 demo paths

[cedRiC874]

Summary

• move the portfolio demo into one shared Python implementation with thin PowerShell and Bash entrypoints
• support strict Windows x86-64 and Linux x86-64 runs with separate locked dependencies, frozen corpora, canonical evidence IDs, and quality profiles
• run the complete Linux x86-64 demo in CI instead of checking only --help
• add an English README and archive the historical root handoff under docs/internal/

Validation

• python -m unittest discover -s tests: 653 passed, 1 skipped
• Windows x86-64 / Python 3.12.13: 50/50 tasks, 21/21 evidence citations, phase5-ci-v1=valid
• Linux x86-64 / Python 3.12.13 with native pip install -r requirements.linux.lock: pip check clean, no pywin32, 50/50 tasks, 21/21 evidence citations, phase5-linux-x86-ci-v1=valid
• Depth-60 frozen plan validation: valid, no network or model calls
• Eval v2 dependency environment: 82 exact pins, valid
• staged diff, YAML, local Markdown links, LF provenance, and shell mode checks passed

Scope boundaries

• macOS, ARM, and 32-bit Python remain explicitly unsupported for the strict frozen-evidence demo
• the original Windows requirements.lock, evals/tasks.jsonl, and frozen commitments remain unchanged
• no online Provider evaluation was run