Refactor insights handling and error encoding in presentation layer

- Updated insights analyzer tests to use Utc for date handling.
- Added timezone support for insights retrieval, allowing insights to be bucketed by the user's local time.
- Introduced `encode_domain_error` for better error handling in API responses.
- Modified various handlers to utilize the new error encoding function.
- Enhanced insights API to reject unknown time zones and return appropriate errors.
- Updated frontend components to handle insights data with timezone awareness.
- Improved localization for insights sample counts.

crates/api-types/src/insights.rs

@@ -17,7 +17,7 @@ pub enum InsightDto {
         sample_count: u32,
     },
     /// `genre`'s share of watches in `month` (1–12) is `multiplier` times the
-    /// uniform 1/12 baseline.
+    /// user's own share of watches in that month.
     Seasonality {
         genre: String,
         month: u32,
@@ -47,3 +47,11 @@ pub enum InsightDto {
 pub struct InsightsResponse {
     pub insights: Vec<InsightDto>,
 }
+
+#[derive(Debug, Clone, Deserialize, utoipa::IntoParams)]
+#[into_params(parameter_in = Query)]
+pub struct InsightsQueryParams {
+    /// IANA time zone (e.g. `Europe/Warsaw`) months, weekdays and hours are
+    /// bucketed in. Defaults to UTC.
+    pub tz: Option<String>,
+}