feat: Implement full network functionality with HTTP and P2P modes

This major update introduces a robust, multi-faceted networking
capability, allowing backups to be managed through a central server or
via direct peer-to-peer connections.

- **Add `serve` command**: Implemented a new `serve` command that runs a
persistent HTTP server. This allows for a centralized backup management
workflow where multiple clients can upload and download archives. -
**HTTP Client Mode**: The `create` and `restore` commands can now
function as HTTP clients, targeting a `serve` instance using the
`ip:port/filename` address format.

- **Restore P2P Mode**: The original peer-to-peer streaming
functionality (where `restore` acts as a TCP server and `create` as a
client) has been fully restored and integrated into the new, more robust
command architecture. - **Accurate Network Progress**: Fixed a critical
bug where network progress bars would not display correctly. The `serve`
command now sends a `Content-Length` header, and `restore` is refactored
to handle asynchronous state updates correctly. - **Smart Address
Parsing**: The application now automatically distinguishes between HTTP
mode (`ip:port/filename`) and P2P mode (`ip:port`), providing a seamless
user experience.

- **Update `README.md`**: The project's README has been completely
rewritten to document all three operating modes (Local, HTTP Server,
P2P) with clear usage examples. - **Add Gitea Actions Workflow**: A new
CI pipeline (`.gitea/workflows/build-and-test.yml`) has been added to
automatically build and test the application on every push and pull
request.

go.mod

@@ -6,7 +6,9 @@ require (
 	github.com/charmbracelet/bubbles v0.21.0
 	github.com/charmbracelet/bubbletea v1.3.4
 	github.com/charmbracelet/lipgloss v1.1.0
+	github.com/gorilla/mux v1.8.1
 	github.com/spf13/cobra v1.9.1
+	golang.org/x/sys v0.30.0
 )
 
 require (
@@ -29,6 +31,5 @@ require (
 	github.com/spf13/pflag v1.0.6 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
 	golang.org/x/sync v0.11.0 // indirect
-	golang.org/x/sys v0.30.0 // indirect
 	golang.org/x/text v0.3.8 // indirect
 )