Add NavMenu settings/presets UI and profile HTTP routes (ticket 011)

Adds thin HTTP routes for profile CRUD and colour-scheme updates
(GET/PATCH /api/settings, GET/POST /api/settings/profiles,
DELETE /api/settings/profiles/:name, POST /api/settings/profiles/:name/activate)
following the existing CSS-route pattern in api.rs, with activate hot-swapping
the running engine's declared params/metrics so switching profiles needs no
restart. Builds out the NavMenu frontend with Settings (colour scheme picker,
CSS import/list/delete) and Presets (list/create/switch/delete profiles with
declaration counts) panels, and a useSettingsPanel hook that applies the
active colour scheme and imported CSS to the document live.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

src/dto.rs

@@ -1,6 +1,7 @@
 use crate::data_value::{MetricPrimitiveKind, RegexToMetricPrimitiveMatcher};
 use crate::metric_primitive::MetricPrimitive;
-use crate::settings::CssEntry;
+use crate::profile::Profile;
+use crate::settings::{ColorScheme, CssEntry, Settings};
 use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
 
@@ -183,3 +184,60 @@ impl From<&CssEntry> for CssEntryDto {
         }
     }
 }
+
+/// Response shape for `GET /api/settings` and `PATCH /api/settings` (ticket
+/// 011): the subset of `Settings` the NavMenu UI needs to render a colour
+/// scheme picker and know which profile is active. `css_entries` is
+/// deliberately omitted here since it already has its own dedicated
+/// `GET /api/settings/css` endpoint (ticket 010).
+#[derive(Debug, Clone, Serialize)]
+pub struct SettingsDto {
+    pub color_scheme: ColorScheme,
+    pub active_profile: Option<String>,
+}
+
+impl From<&Settings> for SettingsDto {
+    fn from(settings: &Settings) -> Self {
+        SettingsDto {
+            color_scheme: settings.color_scheme,
+            active_profile: settings.profiles.active_profile.clone(),
+        }
+    }
+}
+
+/// Request body for `PATCH /api/settings`. Only `color_scheme` is
+/// updatable for now; `None` leaves the current value untouched (so a
+/// partial body doesn't reset other fields).
+#[derive(Debug, Deserialize)]
+pub struct UpdateSettingsRequest {
+    pub color_scheme: Option<ColorScheme>,
+}
+
+/// Summary of one profile for `GET /api/settings/profiles` (ticket 011):
+/// just the name and declaration/dashboard counts the Presets panel needs to
+/// render a list, rather than the full param/metric declaration bodies.
+#[derive(Debug, Clone, Serialize)]
+pub struct ProfileSummaryDto {
+    pub name: String,
+    pub param_count: usize,
+    pub metric_count: usize,
+    pub dashboard_count: usize,
+}
+
+impl From<&Profile> for ProfileSummaryDto {
+    fn from(profile: &Profile) -> Self {
+        ProfileSummaryDto {
+            name: profile.name.clone(),
+            param_count: profile.params.len(),
+            metric_count: profile.metrics.len(),
+            dashboard_count: profile.dashboards.len(),
+        }
+    }
+}
+
+/// Request body for `POST /api/settings/profiles`: creates a new, empty
+/// profile with this name (see `ProfileStore::create`).
+#[derive(Debug, Deserialize)]
+pub struct CreateProfileRequest {
+    pub name: String,
+}