feat(slash): fondation du système de commandes slash pour la CLI custom — #162 (QA verte)

Introduit le contrat unifié des commandes slash consommable par le frontend,
indépendant de la source (native, puis plugin plus tard) :

- domain: modèle pur SlashCommand / SlashCommandSource / SlashCommandAvailability,
  métadonnées UI (nom, description, disponibilité, confirmation requise) et
  validation des noms/préfixes.
- application: registry + list/filter par préfixe + plan d'exécution natif ;
  commandes natives /help et /clean (/clean = nettoyage de la vue de session
  courante ; pas de /reset distinct tant qu'aucune utilité produit ne le justifie).
- backend + app-tauri: exposition du contrat via DTO/transport + tests DTO.

Source neutre : les commandes contribuées par plugins (#165) transiteront par
le même registry sans changer le contrat frontend.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/backend/src/lib.rs

@@ -23,18 +23,19 @@ use application::{
     CreateSprint, CreateTemplate, DeleteAgent, DeleteEmbedderProfile, DeleteIssue, DeleteLayout,
     DeleteMemory, DeleteModelArtifact, DeleteModelServer, DeleteProfile, DeleteSkill, DeleteSprint,
     DeleteTemplate, DescribeEmbedderEngines, DetectAgentDrift, DetectProfiles,
-    DismissEmbedderSuggestion, EnsureLocalModelServer, FirstRunState, GetAppExitWorkGuardState,
-    GetLiveStateLean, GetMemory, GetProjectPermissions, GetProjectSystemPermissions,
-    GetProjectWorkState, GitBranches, GitCheckout, GitCommit, GitGraph, GitInit, GitLog, GitStage,
-    GitStatus, GitUnstage, HarvestMemoryFromTurn, HealthUseCase, ImportChatAttachments,
-    InspectConversation, InstallPluginFromArchive, InstallPluginFromDirectory,
-    JsonPluginManifestValidator, LaunchAgent, LaunchAgentInput, LinkIssues, ListAgents,
-    ListAgentsInput, ListClaudeModels, ListCodexModels, ListDevices, ListEmbedderProfiles,
-    ListIssues, ListLayouts, ListMemories, ListModelServers, ListOpenCodeProviders,
-    ListPluginRuntimeContributions, ListPlugins, ListProfiles, ListProjects, ListResumableAgents,
-    ListSkills, ListSprints, ListTemplates, LiveAgentRegistry, LiveSessions, LiveStateLeanProvider,
-    LiveStateProvider, LiveStateReadProvider, LoadLayout, MarkIssueAttachmentSummarized,
-    McpRuntime, McpToolPermissionCatalogue, MoveTabToNewWindow, MutateLayout, OnnxModelView,
+    DismissEmbedderSuggestion, EnsureLocalModelServer, ExecuteSlashCommand, FirstRunState,
+    GetAppExitWorkGuardState, GetLiveStateLean, GetMemory, GetProjectPermissions,
+    GetProjectSystemPermissions, GetProjectWorkState, GitBranches, GitCheckout, GitCommit,
+    GitGraph, GitInit, GitLog, GitStage, GitStatus, GitUnstage, HarvestMemoryFromTurn,
+    HealthUseCase, ImportChatAttachments, InspectConversation, InstallPluginFromArchive,
+    InstallPluginFromDirectory, JsonPluginManifestValidator, LaunchAgent, LaunchAgentInput,
+    LinkIssues, ListAgents, ListAgentsInput, ListClaudeModels, ListCodexModels, ListDevices,
+    ListEmbedderProfiles, ListIssues, ListLayouts, ListMemories, ListModelServers,
+    ListOpenCodeProviders, ListPluginRuntimeContributions, ListPlugins, ListProfiles, ListProjects,
+    ListResumableAgents, ListSkills, ListSlashCommands, ListSprints, ListTemplates,
+    LiveAgentRegistry, LiveSessions, LiveStateLeanProvider, LiveStateProvider,
+    LiveStateReadProvider, LoadLayout, MarkIssueAttachmentSummarized, McpRuntime,
+    McpToolPermissionCatalogue, MoveTabToNewWindow, MutateLayout, OnnxModelView,
     OpenPluginLayoutWindow, OpenProject, OpenTerminal, OpenTicketAssistant, OrchestratorService,
     PairAttemptLimiter, PairDevice, PermissionProjectorRegistry, PluginCommandTasks,
     PluginConfigDocuments, PluginEventSubscriptions, PluginStorageAccess,
@@ -48,15 +49,15 @@ use application::{
     ResolveMemoryLinks, RestoreOpenWindows, RetryBackgroundTask, ReviewPluginPackage,
     RevokeAllDevices, RevokeDevice, RotateConversationLog, SaveEmbedderProfile, SaveModelServer,
     SaveOpenCodeProviderProfile, SaveProfile, SessionLimitService, SetActiveLayout,
-    SetPluginEnabled, SnapshotOpenWindows, SnapshotRunningAgents, SpawnBackgroundCommand,
-    StopLiveAgent, StructuredRoutingMode, StructuredSessions, SuggestedThisSession,
-    SyncAgentWithTemplate, TerminalSessions, TouchDevice, UnassignSkillFromAgent,
-    UnassignTicketFromSprint, UninstallPlugin, UnlinkIssues, UpdateAgentContext, UpdateAgentEffort,
-    UpdateAgentMcpToolPermissions, UpdateAgentPermissions, UpdateAgentSystemPermissions,
-    UpdateIssue, UpdateIssueCarnet, UpdateLiveState, UpdateMemory, UpdateProjectContext,
-    UpdateProjectMcpToolPermissions, UpdateProjectPermissions, UpdateProjectSystemPermissions,
-    UpdateSkill, UpdateTemplate, WakeSessionProvider, WriteMemory, WriteToTerminal,
-    AGENT_MEMORY_RECALL_BUDGET,
+    SetPluginEnabled, SlashCommandRegistry, SnapshotOpenWindows, SnapshotRunningAgents,
+    SpawnBackgroundCommand, StopLiveAgent, StructuredRoutingMode, StructuredSessions,
+    SuggestedThisSession, SyncAgentWithTemplate, TerminalSessions, TouchDevice,
+    UnassignSkillFromAgent, UnassignTicketFromSprint, UninstallPlugin, UnlinkIssues,
+    UpdateAgentContext, UpdateAgentEffort, UpdateAgentMcpToolPermissions, UpdateAgentPermissions,
+    UpdateAgentSystemPermissions, UpdateIssue, UpdateIssueCarnet, UpdateLiveState, UpdateMemory,
+    UpdateProjectContext, UpdateProjectMcpToolPermissions, UpdateProjectPermissions,
+    UpdateProjectSystemPermissions, UpdateSkill, UpdateTemplate, WakeSessionProvider, WriteMemory,
+    WriteToTerminal, AGENT_MEMORY_RECALL_BUDGET,
 };
 use async_trait::async_trait;
 use domain::ports::{
@@ -877,6 +878,10 @@ impl AgentResumer for AppAgentResumer {
 pub struct BackendCore {
     /// Trivial health use case validating the end-to-end wiring.
     pub health: Arc<HealthUseCase>,
+    /// List/filter the unified slash-command registry.
+    pub list_slash_commands: Arc<ListSlashCommands>,
+    /// Plan execution of a slash command.
+    pub execute_slash_command: Arc<ExecuteSlashCommand>,
     /// Pair a persistent device session.
     pub pair_device: Arc<PairDevice>,
     /// Limits failed pairing attempts.
@@ -1448,6 +1453,9 @@ impl BackendCore {
             Arc::clone(&ids) as Arc<dyn IdGenerator>,
             Arc::clone(&events_port),
         ));
+        let slash_command_registry = SlashCommandRegistry::new();
+        let list_slash_commands = Arc::new(ListSlashCommands::new(slash_command_registry.clone()));
+        let execute_slash_command = Arc::new(ExecuteSlashCommand::new(slash_command_registry));
         let pair_device = Arc::new(PairDevice::new(
             Arc::clone(&device_session_port),
             Arc::clone(&ids) as Arc<dyn IdGenerator>,
@@ -2924,6 +2932,8 @@ impl BackendCore {
 
         Self {
             health,
+            list_slash_commands,
+            execute_slash_command,
             pair_device,
             pair_attempt_limiter: Arc::clone(&pair_attempt_limiter_port),
             authenticate_session,