fix: harden Windows bootstrap installer

[mihir-28]

Summary

Fixes Windows install/bootstrap failures found while installing Codex SEO on Python 3.13/3.14 systems.

Changes

• Prefer supported Python versions 3.10-3.13 and avoid Python 3.14 for now, because some runtime dependencies are not fully ready there.
• Add local-checkout install mode so running install.ps1 or install.sh from the repo installs the current working tree instead of downloading the old tagged release.
• Improve Windows bootstrap diagnostics so failed required steps print useful errors.
• Make bootstrap JSON parsing tolerant of noisy stdout before JSON.
• Suppress noisy dependency import output during environment verification.
• Report unwritable cache/output paths in verifier notes.
• Add regression tests for Python version selection, bootstrap diagnostics, noisy verifier JSON, and unwritable path reporting.

Why

On Windows, the installer previously:

• selected Python 3.14 when present, then dependency setup could fail;
• downloaded the tagged release even when testing local fixes;
• could fail with Codex SEO runtime bootstrap failed without actionable diagnostics;
• treated WeasyPrint's native-library banner as JSON parse failure.

After these changes, the install reaches a usable runtime and clearly reports optional PDF/report dependency issues.

Verification

• install.ps1 PowerShell parse: OK
• scripts/bootstrap_environment.py and scripts/verify_environment.py compile with Python 3.13
• Local bootstrap returns ok=true
• Environment verifier returns:
  • Core ready: YES
  • Visual ready: YES
  • Premium-report ready: YES after MSYS2 Pango + WEASYPRINT_DLL_DIRECTORIES
  • Full ready: YES