Fix Windows installer clean-machine Python setup

[LuisMRaimundo]

Summary

Makes the Windows installer work on a clean Windows 10/11 x64 machine (no Python, Tesseract, or Poppler). Base: current main.

Root cause

The installer only worked where Python/Tesseract/Poppler already existed. The clean-machine route relied on a fragile custom-TargetDir Python install (which silently fails into repair mode when a Python already exists) and installed packages into that interpreter directly. There was no guaranteed project environment.

Fix: managed Python + project-local venv

• Python hierarchy: detect valid existing Python (py launcher / PATH / registry / per-user locations); else Install managed Python (default) using the official python.org installer in normal per-user mode (no fragile TargetDir), then locate it.
• Always create a project-local venv at installers/runtime/windows/venv and install requirements.txt into it.
• Launch uses the venv Python (venv\Scripts\python.exe).
• Custom Python is advanced-only, never default, never C:\Python; validated (3.10+, pip, tkinter) before continuing with the exact failing condition.

Wizard

Python page now has 3 explicit options: Recommended: managed, Use detected compatible Python, Advanced: custom. Managed is selected by default when no compatible Python is detected.

Policies

• Process-local PATH by default (prepends venv\Scripts, base Python, Tesseract, Poppler); user/system PATH opt-in only.
• Tesseract/Poppler failures are warning-only; GUI still launches. Python/tkinter/pip/packages is hard-fail.
• gui_ready derives from venv validation, independent of OCR capability.

install_state.json

Records python_mode (managed_installed/detected_existing/custom), base_python_path, venv_python_path, packages_installed, tesseract_mode/tesseract_path, poppler_mode/poppler_bin_path, path_policy, gui_ready, ocr_capability, install_timestamp, installer_version.

Tests

• python -m unittest discover -s tests -v -> 50 passed
• installers\windows\tests\Run-InstallerTests.bat -> 51 passed

Manual clean-machine test

1. On a clean Windows 10/11 x64 VM (no Python/Tesseract/Poppler), remove any old Text-seeker folder.
2. Download this PR branch ZIP and extract to a simple path (e.g. C:\ts).
3. Run installers\windows\Install and Run.bat.
4. Leave Install managed Python selected; finish the wizard; click Install.
5. Confirm the GUI opens.
6. Run doctor:
   installers\runtime\windows\venv\Scripts\python.exe installers\common\bootstrap.py doctor
7. Report installers\runtime\windows\install.log (and python-installer.log).