chore: migrate from GitLab to Gitea

- Update module path from gitlab.com/unboundsoftware/storage to
  git.unbound.se/unboundsoftware/storage
- Update import examples in documentation (CLAUDE.md, README.md)
- Remove .gitlab-ci.yml (GitLab CI pipeline no longer needed)
- Remove gitlab-ci-linter pre-commit hook
- Update go-imports local path in pre-commit config

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -14,7 +14,7 @@ Shared storage utilities for AWS S3.
 ### Using the Upload Manager (recommended for large files)
 
 ```go
-import "gitlab.com/unboundsoftware/storage"
+import "git.unbound.se/unboundsoftware/storage"
 
 // Create storage with automatic AWS config loading
 s3Storage, err := storage.New("my-bucket")
@@ -31,7 +31,7 @@ url, err := s3Storage.Store("path/to/file.pdf", fileReader, "application/pdf")
 ```go
 import (
     "github.com/aws/aws-sdk-go-v2/config"
-    "gitlab.com/unboundsoftware/storage"
+    "git.unbound.se/unboundsoftware/storage"
 )
 
 // Load custom AWS config