feat(Common/SCM): Add DTO for updating SCM provider properties

Introduces `SourceControlUpdateDTO` struct in the Common crate to facilitate updates to SCM provider properties. This DTO will be used across the Land architecture for:

1. Propagating UI state changes (commit message input box value) from `Wind/Sky` components to `Mountain` via Tauri events
2. Synchronizing badge counts between `Cocoon` extensions and the native backend via `Vine` gRPC
3. Enabling the SCM workflow (#8) by allowing updates to provider-specific properties

The DTO includes optional fields for `InputBoxValue` and `Count` with `ProviderHandle` identification, using `serde` attributes for PascalCase serialization. This aligns with our trait-based architecture where:
- `Common` defines the data contract
- `Mountain` implements state persistence in `AppState`
- `Cocoon` will use this for extension communication
- `Wind` services will consume/produce this DTO

Completes the SCM DTO foundation started in recent commits (Refs 00f54f8, 4c0cc70).

Author: NikolaRHristov

Source/SourceControlManagement/DTO/SourceControlUpdateDTO.rs

@@ -0,0 +1,22 @@
+//! # SourceControlUpdateDTO
+//!
+//! Defines a generic DTO for updating properties of an SCM provider.
+
+use serde::{Deserialize, Serialize};
+
+/// A serializable struct used to send updates for a source control provider's
+/// top-level properties, such as the commit message in the input box or the
+/// badge count.
+#[derive(Serialize, Deserialize, Debug, Clone)]
+#[serde(rename_all = "PascalCase")]
+pub struct SourceControlUpdateDTO {
+	/// The handle of the provider to update.
+	pub ProviderHandle:u32,
+	/// The new value for the commit message input box.
+	#[serde(skip_serializing_if = "Option::is_none")]
+	pub InputBoxValue:Option<String>,
+	/// The new count to display as a badge on the SCM icon.
+	#[serde(skip_serializing_if = "Option::is_none")]
+	pub Count:Option<u32>,
+	// This could be expanded to include other updatable properties.
+}