Add universal uv-based installer for OG-Core and country repos

[SeaCelo]

This adds a from-scratch installer that takes a user from a bare machine (only git required) to a working OG model environment: it installs uv, clones the repo you pick, runs uv sync --extra dev, and verifies the import.

• scripts/install.sh (macOS/Linux) and scripts/install.ps1 (Windows) are universal — choose the repo from a menu or pass --repo / -Repo. The catalog has og-core and og-eth today; more country calibrations get added as they migrate to uv.
• scripts/QUICK_INSTALL.md documents both ways to run it (one-line, or download-and-run), per platform.

cc: @rickecon @jdebacker

[SeaCelo]

Fixed a problem with the windows command because of how it ran the script from memory. We now download the script to a temp file and run it. Thanks @utsinboots

To test this from the PR branch on SeaCelo (until this lands):

macOS / Linux

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/SeaCelo/OG-Core/installer/scripts/install.sh)" _ --repo og-core

Windows (PowerShell)

$f = "$env:TEMP\og-install.ps1"; irm https://raw.githubusercontent.com/SeaCelo/OG-Core/installer/scripts/install.ps1 -OutFile $f; powershell -ExecutionPolicy Bypass -File $f -Repo og-core

Installs OG-Core into a directory you choose (~1-2 min). Omit --repo og-core / -Repo og-core to pick from the menu instead, or use og-eth once its uv migration lands. After merge, swap the branch for master in the URLs.

[utsinboots]

I tested the windows installer and can confirm it runs with all checks passed successfully:

• install uv
• clone og-core
• install og-core (uv sync)
• verify installation

[jdebacker]

@SeaCelo Nice addition to add this command line install utility. Merging.