feat(sdk,plugins): ajoute capability tooling et services runtime publics (workspace/terminal/tasks)

- capability manifeste tooling supportée backend + transport runtime catalog
- ctx.services publique côté SDK/runtime, gated par tooling
- surface honnête: workspace, terminal, et tasks en observation/contrôle uniquement
- docs/exemple/tests mis à jour
- QA PASS sur feature/sdk-plugin-tooling-build-debug-surface

crates/backend/src/dto.rs

@@ -239,6 +239,8 @@ pub struct PluginRuntimePluginDto {
     pub icon_url: Option<String>,
     /// Content hash.
     pub content_hash: String,
+    /// Public manifest capabilities.
+    pub capabilities: Vec<domain::PluginCapability>,
     /// Contributions.
     pub contributes: domain::PluginContributionSet,
 }
@@ -265,6 +267,7 @@ impl From<application::PluginRuntimePlugin> for PluginRuntimePluginDto {
             bundle_url: value.bundle_url,
             icon_url: value.icon_url,
             content_hash: value.content_hash,
+            capabilities: value.capabilities,
             contributes: value.contributes,
         }
     }