refactor: use value semantics for GitHub and Codeberg clients

- Changed github.NewClient() to return Client instead of *Client
- Changed codeberg.NewClient() to return Client instead of *Client
- Updated sync_handlers.go to handle value semantics properly
- Both clients only contain immutable string fields, making value semantics more appropriate

docs: add comprehensive documentation

- Added doc/ directory with full documentation
- Created architecture overview explaining system design
- Added complete API reference for all packages, types, and functions
- Created configuration guide with examples
- Added usage examples and common workflows
- Created development guide for contributors
- Updated README with links to documentation

🤖 Generated with [Claude Code](https://claude.ai/code)

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

1 files changed, 2 insertions, 3 deletions

diff --git a/internal/codeberg/codeberg.go b/internal/codeberg/codeberg.go
index 288d1e7..4f0a76d 100644
--- a/internal/codeberg/codeberg.go
+++ b/internal/codeberg/codeberg.go
@@ -30,10 +30,9 @@ type Client struct {
 	org     string
 }
 
-// CLAUDE: Is there a rason, that we return a pointer of Client?
 // NewClient creates a new Codeberg API client
-func NewClient(org string) *Client {
-	return &Client{
+func NewClient(org string) Client {
+	return Client{
 		baseURL: "https://codeberg.org/api/v1",
 		org:     org,
 	}