clean(presentation): strip comments, kill dead code, extract constants

- remove all doc/inline comments
- delete unused ApiError variants (AuthRequired, NotImplemented) and helpers (internal, not_implemented)
- prefix lifetime-only AppState fields with _ to suppress dead_code warning
- extract magic numbers: TICK_INTERVAL_SECS, EXPIRY_THRESHOLD_HOURS, POLL_INTERVAL_SECS, EVENT_BUS_CAPACITY, DEFAULT_ACTIVITY_LIMIT, DEFAULT_SEARCH_LIMIT, etc
- replace inline serde_json::json! in sync_status with typed SyncStatusEntry
- fix mid-file import in schedule handler
- fix extractors: strip_prefix instead of magic offset 6
- fix unreachable pattern in wire_repositories with cfg guard
- use eq_ignore_ascii_case for content-type header check

crates/presentation/src/handlers/admin.rs

@@ -1,5 +1,3 @@
-//! Admin handlers.
-
 use axum::Json;
 use axum::extract::{Query, State};
 use serde::Deserialize;
@@ -12,7 +10,8 @@ use crate::errors::ApiError;
 use crate::extractors::AdminUser;
 use crate::state::AppState;
 
-/// GET /admin/settings
+const DEFAULT_ACTIVITY_LIMIT: u32 = 50;
+
 pub async fn get_settings(
     State(state): State<AppState>,
     AdminUser(_user): AdminUser,
@@ -23,7 +22,6 @@ pub async fn get_settings(
     Ok(Json(SettingsResponse { settings }))
 }
 
-/// PUT /admin/settings
 pub async fn update_settings(
     State(state): State<AppState>,
     AdminUser(_user): AdminUser,
@@ -35,7 +33,6 @@ pub async fn update_settings(
     };
     application::admin::update_settings::execute(&state.admin_deps, cmd).await?;
 
-    // Re-read after update
     let pairs =
         application::admin::get_settings::execute(&state.admin_deps, GetSettingsQuery).await?;
     let settings: HashMap<String, String> = pairs.into_iter().collect();
@@ -47,14 +44,13 @@ pub struct ActivityLogParams {
     pub limit: Option<u32>,
 }
 
-/// GET /admin/activity
 pub async fn get_activity_log(
     State(state): State<AppState>,
     AdminUser(_user): AdminUser,
     Query(params): Query<ActivityLogParams>,
 ) -> Result<Json<Vec<ActivityEventResponse>>, ApiError> {
     let query = GetActivityLogQuery {
-        limit: params.limit.unwrap_or(50),
+        limit: params.limit.unwrap_or(DEFAULT_ACTIVITY_LIMIT),
     };
     let events = application::admin::activity_log::execute(&state.admin_deps, query).await?;
     Ok(Json(