fix(updater,install,docs): follow the move to FelisMC/Felis (#53)

The repository moved to FelisMC/Felis, but the felis-api release coordinate, the installer's default FELIS_REPO_URL, the PaperMC user-agent strings and both READMEs still named MliroLirrorsIngenuity/Felis. Live on the audit box, 'felis update' reported 'github: MliroLirrorsIngenuity/Felis releases/latest returned HTTP 404 -- ...', pointing operators at a coordinate that no longer exists; the old path keeps answering today only because GitHub still 301s the transfer (verified with a read token against api.github.com: old path 301, new path 200), and if that redirect is ever retired every install and every update check breaks with it.

Replace the coordinate in the six tracked files: the updater topology and both test fixtures, the bootstrap default URL and user-agent strings, and README.md/README_EN.md. Green live: the same command now reports 'github: FelisMC/Felis releases/latest returned HTTP 404 -- ...' (still 404 because the new home has published no stable release yet -- a release-process fact, not a code bug).

Gates: gofmt, go vet, go test ./..., deploy/bootstrap_test.sh all clean.

README_EN.md

@@ -29,7 +29,7 @@ Table of Contents
 On a prepared Linux host, run:
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MliroLirrorsIngenuity/Felis/main/deploy/bootstrap.sh | sudo bash
+curl -fsSL https://raw.githubusercontent.com/FelisMC/Felis/main/deploy/bootstrap.sh | sudo bash
 ```
 
 The script installs K3s, deploys the control plane, and launches a setup wizard. Once done, open your browser at the configured domain.