feat: first cut at dev brain

src/app/view/preferences.rs

@@ -156,6 +156,33 @@ impl App {
             ]
             .spacing(10),
         );
+        let dev_brain_group = preference_group(
+            PreferenceSection::DevBrain,
+            "DEV BRAIN",
+            column![
+                hint(
+                    checkbox(self.preference_draft.dev_brain_enabled)
+                        .label("Enable project-backed LLM wiki")
+                        .on_toggle(Message::PreferenceDevBrainEnabledChanged),
+                    "Adds validated search, read, and batch-publication tools for a dedicated Obsidian vault. Disabled means no Dev Brain tools or prompt instructions.",
+                ),
+                row![
+                    text_input(
+                        "/path/to/Obsidian vault",
+                        &self.preference_draft.dev_brain_vault_path,
+                    )
+                    .on_input(Message::PreferenceDevBrainVaultChanged)
+                    .padding(9)
+                    .width(Length::Fill),
+                    action_button("Choose…").on_press(Message::ChooseDevBrainVault),
+                ]
+                .spacing(8)
+                .align_y(Alignment::Center),
+                text("The folder must already contain .obsidian. DS4Server manages only its declared wiki pages and leaves settings, attachments, hidden files, and unrelated notes untouched.")
+                    .size(12),
+            ]
+            .spacing(10),
+        );
         let generation_group = preference_group(
             PreferenceSection::Generation,
             "GENERATION",
@@ -552,6 +579,7 @@ impl App {
         let mut fields = column![
             model_group,
             endpoint_group,
+            dev_brain_group,
             generation_group,
             execution_group,
             acceleration_group,