Add Vanilla Tweaks auto-install from extras/datapacks/

Place datapacks_<ver>.zip or crafting_tweaks_<ver>.zip in extras/datapacks/
before running the Minecraft installer and they will be detected automatically.

- Pattern match: *datapack* → unzip into datapacks-download/; *craft* → copy as-is
- Version extracted from filename; compared against selected MC version at picker step
- Early banner notice when ZIPs are absent (where to put them and naming convention)
- If ZIPs present: show found files + version check, offer "Use pre-packaged VT?" (default y)
- Accepting skips the individual datapack picker entirely
- Manual fallback instructions updated to hint at extras/datapacks/ for next time
- Removed broken VT share# links from manual instructions
- Added extras/datapacks/README.md (naming convention + download sources)
- Added .gitignore: extras/datapacks/*.zip never committed

https://claude.ai/code/session_019XgsQ13XKm4Zj3cNsDNwHj

extras/datapacks/README.md

@@ -0,0 +1,34 @@
+# Vanilla Tweaks — place your ZIPs here
+
+The Minecraft installer detects ZIPs in this folder and offers to install them
+automatically. No manual SCP or unzipping required.
+
+## Naming convention
+
+The installer uses filename patterns, so the name must include the right keyword:
+
+| File type | Pattern (case-insensitive) | Example |
+|-----------|---------------------------|---------|
+| Datapacks | filename contains `datapack` | `datapacks_1.21.zip` |
+| Crafting tweaks | filename contains `craft` | `crafting_tweaks_1.21.zip` |
+
+Include the Minecraft version number in the filename so the installer can warn
+you if the ZIP version does not match the server version.
+
+## Where to download
+
+Go to <https://vanillatweaks.net/picker/datapacks/> and
+<https://vanillatweaks.net/picker/crafting-tweaks/>, select your MC version,
+choose your packs, and download the ZIP.
+
+## What the installer does
+
+- **Datapacks ZIP** — unzipped into `<instance>/datapacks-download/`; the itzg
+  image auto-installs the individual `.zip` files from `/datapacks/` on startup.
+- **Crafting tweaks ZIP** — copied as-is into `<instance>/datapacks-download/`;
+  the itzg image handles it the same way.
+
+## Cleanup
+
+ZIPs in this folder are gitignored so they are never committed to the repo.
+Delete them after the server is set up, or keep them for the next fresh install.