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

Author: marcelolafleur

scripts/QUICK_INSTALL.md

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+# Quick install
+
+A single installer for OG-Core and its country calibrations. Pre-req: **git** installed. Nothing else.
+
+It installs uv if needed, clones the repo you choose, runs `uv sync --extra dev`, and verifies the import. Pick the repo from a menu, or pass `--repo` / `-Repo`.
+
+You can run it two ways — paste a one-line command, or download the script and run it. Both do the same thing.
+
+## Option 1 — One-line
+
+### macOS / Linux
+
+```bash
+/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/PSLmodels/OG-Core/master/scripts/install.sh)"
+```
+
+### Windows (PowerShell)
+
+```powershell
+$f = "$env:TEMP\og-install.ps1"; irm https://raw.githubusercontent.com/PSLmodels/OG-Core/master/scripts/install.ps1 -OutFile $f; powershell -ExecutionPolicy Bypass -File $f
+```
+
+(On Windows the installer is saved to a temp file and run from there, so it executes as a normal script.)
+
+## Option 2 — Download, then run
+
+Handy if you'd rather read the script first, or keep it to re-run later.
+
+### macOS / Linux
+
+```bash
+curl -fsSL https://raw.githubusercontent.com/PSLmodels/OG-Core/master/scripts/install.sh -o install.sh
+bash install.sh
+```
+
+### Windows (PowerShell)
+
+```powershell
+Invoke-WebRequest -UseBasicParsing -Uri https://raw.githubusercontent.com/PSLmodels/OG-Core/master/scripts/install.ps1 -OutFile install.ps1
+powershell -ExecutionPolicy Bypass -File .\install.ps1
+```
+
+## Choosing a repo and skipping prompts
+
+By default the installer shows a menu of repos and prompts for a destination. Flags let you go straight there — they work with either method above:
+
+- `--repo` / `-Repo` — a short key for a repo in the built-in catalog:
+  - `og-core` — base model ([PSLmodels/OG-Core](https://github.com/PSLmodels/OG-Core))
+  - `og-eth` — Ethiopia calibration ([EAPD-DRB/OG-ETH](https://github.com/EAPD-DRB/OG-ETH)); works once its uv migration lands
+- `--repo-url` / `-RepoUrl` — a full git URL, for any other uv-based repo (a fork, or a country repo not yet in the catalog). Clones the default branch.
+- `--branch` / `-Branch` — **for development work**: install a non-default branch (e.g. a fork or a migration branch before it merges).
+- `--dest` / `-Dest` and `--yes` / `-Yes` — set the parent directory and skip the confirmation prompt.
+
+```bash
+# macOS / Linux -- OG-Core to ~/Projects/OG-Core, no prompts
+bash install.sh --repo og-core --dest ~/Projects --yes
+# any repo by URL (default branch)
+bash install.sh --repo-url https://github.com/OWNER/OG-XYZ.git
+# a specific branch (development)
+bash install.sh --repo-url https://github.com/OWNER/OG-XYZ.git --branch my-feature
+```
+
+```powershell
+# Windows -- OG-Core to C:\Users\<you>\Projects\OG-Core, no prompts
+powershell -ExecutionPolicy Bypass -File .\install.ps1 -Repo og-core -Dest C:\Users\$env:USERNAME\Projects -Yes
+# any repo by URL (default branch)
+powershell -ExecutionPolicy Bypass -File .\install.ps1 -RepoUrl https://github.com/OWNER/OG-XYZ.git
+```
+
+More country calibrations get added to the catalog as they migrate to uv.
+
+## After install
+
+Activate the venv and you're set:
+
+```bash
+# macOS / Linux
+cd <destination>
+source .venv/bin/activate
+python -W ignore -c "import ogcore; print(ogcore.__version__)"
+```
+
+```powershell
+# Windows
+cd <destination>
+.\.venv\Scripts\Activate.ps1
+python -W ignore -c "import ogcore; print(ogcore.__version__)"
+```
+
+(Swap `ogcore` for the package of the repo you installed — e.g. `ogeth` for OG-ETH.)