Add ServerCatPremium tweaks, build files and docs

ServerCatPremium_/index.md

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+# ServerCatPremium (legacy — iOS 15)
+
+Unlocks premium features in ServerCat by forcing `isPremiumActive` (`sub_100454D70`) to always return `1`.
+
+- **App**: [ServerCat – SSH Terminal](https://apps.apple.com/us/app/servercat-ssh-terminal/id1501532023)
+- **Tested on**: ServerCat 1.6.4, iOS 15.8.6
+- **Note**: ServerCat 1.6.4 is the last version supporting iOS 15. Latest requires iOS 17+.
+
+## Build
+
+```sh
+make clean && make package THEOS_PACKAGE_SCHEME=rootless DEBUG=0
+```
+
+## Inject
+
+```sh
+cyan -i tech.baye.servercat-1.6.4.ipa \
+     -o tech.baye.servercat-1.6.4_patched.ipa \
+     -f xyz.nohamr_1.0.0-1_iphoneos-arm64.deb \
+     -u
+```