Standardize on Python 3.13 (matches prod 3.13.7)

Prod runs Python 3.13.7, not the originally planned 3.12. Align the
stack: CI both jobs 3.12->3.13, the IIS install runbook and the dev
setup guide to 3.13 (winget Python.Python.3.13). NOTE for whoever
maintains the offline kit: its wheels are still cp312 and must be
regenerated as cp313 before the next air-gapped deploy.

docs/DEVELOPMENT-SETUP.md

@@ -23,7 +23,7 @@ sane, then use manual for day-to-day work.
 
 | Need | Version | Check |
 | --- | --- | --- |
-| Python | 3.12 (64-bit) | `python --version` |
+| Python | 3.13 (64-bit) - matches prod + CI | `python --version` |
 | Node.js | 18+ | `node --version` |
 | MySQL | 8.0 (or Docker, below) | `mysql --version` |
 | Git | any recent | `git --version` |
@@ -33,7 +33,7 @@ reopen the terminal so PATH updates):
 
 ```powershell
 winget install Git.Git                    # includes Git Bash (naming hook needs it)
-winget install Python.Python.3.12
+winget install Python.Python.3.13
 winget install OpenJS.NodeJS.LTS          # LTS; may install v24, fine for this SPA
 winget install Microsoft.VisualStudioCode
 winget install Oracle.MySQL               # or Docker.DockerDesktop for the DB