feat(backend,frontend): lot utilisateur #310 #311 #312 #313 — horodatage conversation, stop agent robuste, préférence terminal par défaut, paramètres projet (QA verte)

- #310: horodatage de tous les messages et événements de conversation visibles — composant partagé EntryTimestamp, timestamps propagés dans le transcript chat, les annonces inter-agent et le viewer de conversation, normalisation côté domain/adapters (conversation_log, paginate).
- #311: stop d'agent robuste pour PTY non monté, sessions headless et CLI custom — lifecycle/orchestrator durcis, ponts chat app-tauri/web-server alignés, arrêt fiable sans session orpheline.
- #312: préférence globale d'interface terminal par défaut — nouveau store settings (domain/application/infrastructure + tests), DTO et commandes backend, adapter frontend userSettings, panneau TerminalSettings dans les paramètres globaux.
- #313: Paramètres du projet — contexte de projet éditable et couleur de thème par projet (ProjectSettingsPanel + projectTheme), teinte des onglets projet, persistance via DTO projet.

QA verte (GO QA sur feature/batch-310-311-312-313-chat-stop-prefs-theme) — vérifications Git: git diff --cached --check OK; staging borné à crates/ et frontend/ (74 fichiers, +2105/-531), commit unique de lot conforme à la convention des lots (précédents batch-151/158/159, batch-210/211/212) car les fichiers partagés (dto.rs, commands.rs, CustomAgentChatView) entrelacent les 4 tickets.

fichiers .ideai/* (agents/test.md, chat-drafts.json, system-permissions.json, tickets/counter.json, tickets/index.json, tickets/308-313/), attachments/ et scripts/ hors périmètre et préservés en worktree ; aucun push.

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

crates/domain/src/settings.rs

@@ -0,0 +1,69 @@
+//! Machine-local user preferences and project-owned presentation settings.
+
+use serde::{Deserialize, Serialize};
+
+/// Preferred interface when a new human-facing agent terminal is opened.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum DefaultAgentTerminalInterface {
+    /// Provider's native interactive terminal UI.
+    NativeTui,
+    /// IdeA's structured/custom CLI chat surface.
+    IdeaCli,
+}
+
+/// Global, machine-local IdeA preferences.
+#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct IdeaUserSettings {
+    /// Default for newly launched human-facing agent terminals.
+    #[serde(default)]
+    pub default_agent_terminal_interface: Option<DefaultAgentTerminalInterface>,
+}
+
+/// Strict project theme colour (`#RRGGBB`).
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(try_from = "String", into = "String")]
+pub struct ThemeColor(String);
+
+impl ThemeColor {
+    /// Validates and builds a project theme colour.
+    pub fn new(value: impl Into<String>) -> Result<Self, String> {
+        let value = value.into();
+        let valid = value.len() == 7
+            && value.starts_with('#')
+            && value.as_bytes()[1..].iter().all(u8::is_ascii_hexdigit);
+        valid
+            .then_some(Self(value))
+            .ok_or_else(|| "themeColor must match #RRGGBB".to_owned())
+    }
+
+    /// Returns the validated wire representation.
+    #[must_use]
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+}
+
+impl TryFrom<String> for ThemeColor {
+    type Error = String;
+
+    fn try_from(value: String) -> Result<Self, Self::Error> {
+        Self::new(value)
+    }
+}
+
+impl From<ThemeColor> for String {
+    fn from(value: ThemeColor) -> Self {
+        value.0
+    }
+}
+
+/// Settings owned by one project and stored below its `.ideai` directory.
+#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ProjectSettings {
+    /// Optional visual theme colour; absence keeps the product fallback.
+    #[serde(default)]
+    pub theme_color: Option<ThemeColor>,
+}