fix: include PowerShell files in diff inventory

[Hughhhhcoder]

Summary

Fixes #706. Diff-scan inventories currently omit changed PowerShell files because the shared text-code extension set does not include .ps1. This prevents valid locations in PowerShell files from being recorded as in-scope candidates.

Changes

• Add .ps1 to the existing text-code extension set used by diff inventories.
• Add a regression test that creates a synthetic Git repository, changes a JSON file and a PowerShell file, and verifies that both appear in the revision inventory.

Testing

• uv run --project plugins/codex-security --extra test pytest -q plugins/codex-security/tests/test_generate_in_scope_files.py plugins/codex-security/tests/test_rank_preview.py — 57 passed
• ruff check plugins/codex-security/scripts/rank_preview.py plugins/codex-security/tests/test_generate_in_scope_files.py — passed
• python3 -m py_compile plugins/codex-security/scripts/rank_preview.py plugins/codex-security/tests/test_generate_in_scope_files.py — passed
• git diff --check — passed

Risk and rollout

This is a small compatibility fix with no public CLI or API changes. It only expands the existing diff inventory language allowlist to include PowerShell files; normal inventory behavior and other extension handling are unchanged.

Public disclosure review

• No customer, partner, prospect, or user identities, data, or identifying details are included.
• No credentials, personal data, private source, scan findings, or nonpublic links or tickets are included.
• I reviewed the branch name, title, description, commits, changes, comments, logs, screenshots, attachments, and links for public disclosure.

[Hughhhhcoder]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Delightful!

Reviewed commit: 9214f8ed22

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