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/channels.rs

@@ -1,5 +1,3 @@
-//! Channel CRUD handlers.
-
 use axum::Json;
 use axum::extract::{Path, State};
 
@@ -20,7 +18,6 @@ use crate::errors::ApiError;
 use crate::extractors::CurrentUser;
 use crate::state::AppState;
 
-/// GET /channels
 pub async fn list_channels(
     State(state): State<AppState>,
     CurrentUser(_user): CurrentUser,
@@ -30,7 +27,6 @@ pub async fn list_channels(
     Ok(Json(channels.into_iter().map(ChannelResponse::from).collect()))
 }
 
-/// GET /channels/mine
 pub async fn list_my_channels(
     State(state): State<AppState>,
     CurrentUser(user): CurrentUser,
@@ -43,7 +39,6 @@ pub async fn list_my_channels(
     Ok(Json(channels.into_iter().map(ChannelResponse::from).collect()))
 }
 
-/// POST /channels
 pub async fn create_channel(
     State(state): State<AppState>,
     CurrentUser(user): CurrentUser,
@@ -58,7 +53,6 @@ pub async fn create_channel(
     Ok(Json(ChannelResponse::from(channel)))
 }
 
-/// GET /channels/:id
 pub async fn get_channel(
     State(state): State<AppState>,
     CurrentUser(_user): CurrentUser,
@@ -71,7 +65,6 @@ pub async fn get_channel(
     Ok(Json(ChannelResponse::from(channel)))
 }
 
-/// PUT /channels/:id
 pub async fn update_channel(
     State(state): State<AppState>,
     CurrentUser(user): CurrentUser,
@@ -108,7 +101,6 @@ pub async fn update_channel(
     Ok(Json(ChannelResponse::from(channel)))
 }
 
-/// DELETE /channels/:id
 pub async fn delete_channel(
     State(state): State<AppState>,
     CurrentUser(user): CurrentUser,
@@ -122,9 +114,6 @@ pub async fn delete_channel(
     Ok(axum::http::StatusCode::NO_CONTENT)
 }
 
-// ── Config snapshots ─────────────────────────────────────────────────────
-
-/// POST /channels/:id/snapshots
 pub async fn save_snapshot(
     State(state): State<AppState>,
     CurrentUser(_user): CurrentUser,
@@ -138,7 +127,6 @@ pub async fn save_snapshot(
     Ok(Json(ConfigSnapshotResponse::from(snap)))
 }
 
-/// GET /channels/:id/snapshots
 pub async fn list_snapshots(
     State(state): State<AppState>,
     CurrentUser(_user): CurrentUser,
@@ -149,7 +137,6 @@ pub async fn list_snapshots(
     Ok(Json(snaps.into_iter().map(ConfigSnapshotResponse::from).collect()))
 }
 
-/// GET /channels/:id/snapshots/:snapshot_id
 pub async fn get_snapshot(
     State(state): State<AppState>,
     CurrentUser(_user): CurrentUser,
@@ -165,7 +152,6 @@ pub async fn get_snapshot(
     Ok(Json(ConfigSnapshotResponse::from(snap)))
 }
 
-/// PATCH /channels/:id/snapshots/:snapshot_id
 pub async fn patch_snapshot(
     State(state): State<AppState>,
     CurrentUser(_user): CurrentUser,
@@ -184,7 +170,6 @@ pub async fn patch_snapshot(
     Ok(Json(ConfigSnapshotResponse::from(snap)))
 }
 
-/// POST /channels/:id/snapshots/:snapshot_id/restore
 pub async fn restore_snapshot(
     State(state): State<AppState>,
     CurrentUser(_user): CurrentUser,