build(Mountain): add base64 dependency for encoding needs

Added the base64 v0.22.1 crate to support upcoming encoding/decoding requirements in the Mountain backend. This aligns with Land's need to handle:
- RPC payload serialization in the Vine IPC layer
- Potential binary data handling in extension communication via Cocoon
- File content encoding for River/Sun filesystem operations

The selection of a maintained version ensures compatibility with Tauri's security requirements while providing modern encoding APIs. This foundational dependency will be used in future work for persistent state serialization and extension host protocol compliance.

Author: NikolaRHristov

Cargo.toml

@@ -29,6 +29,7 @@ tauri = { version = "2.5.1", features = [
 tokio = { workspace = true }
 tokio-tungstenite = { workspace = true }
 unbug = { workspace = true }
+base64 = "0.22.1"
 
 [features]
 Debug = []