feat: read & upload history (0.19.0)

Per-user reading progress and uploader attribution.

Schema (migration 0011): `read_progress` table (one row per (user,
manga); chapter_id nullable on chapter delete) and nullable
`uploaded_by` columns on mangas + chapters with partial indexes
scoped to non-null rows.

Endpoints (all `/me/*`, auth-scoped):
- PUT `/v1/me/read-progress` upserts. FK violations + cross-manga
  chapter ids both surface as 4xx (404 / 422) so the API can't be
  used to write logically invalid rows.
- GET `/v1/me/read-progress` paged newest-first list.
- GET `/v1/me/read-progress/:manga_id` enriched with chapter_number
  for the manga page's Continue CTA.
- DELETE `/v1/me/read-progress/:manga_id` idempotent.
- GET `/v1/me/uploads` interleaved manga + chapter uploads as a
  tagged union; limit-only pagination.

Existing manga + chapter upload handlers stamp `uploaded_by`.

Frontend:
- Reader emits progress on mount + page change (debounce) and via
  IntersectionObserver in continuous mode. High-water mark is seeded
  from the persisted server value so re-opening a chapter doesn't
  regress to page 1. Tab close survives via `sendBeacon` (fallback
  `keepalive` fetch); SPA navigation flushes via regular fetch.
- Manga detail page shows "Continue reading Chapter N — page M"
  above the chapters list, working even for mangas with >50
  chapters.
- New `/profile/history` tab with reading history (clear-per-row,
  inline error on failure) and uploads (mangas + chapters mixed
  chronologically with type-aware rendering).

171 backend tests (incl. 16 history tests covering ownership, FK
race, cross-link guard, chapter SET NULL behaviour) and 97 frontend
tests + svelte-check clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/domain/upload_entry.rs

@@ -0,0 +1,40 @@
+use chrono::{DateTime, Utc};
+use serde::Serialize;
+use uuid::Uuid;
+
+use super::chapter::Chapter;
+use super::manga::Manga;
+
+/// Tagged union used by `GET /me/uploads` to interleave manga + chapter
+/// rows chronologically. Serialised as `{ "kind": "...", ... }` so a
+/// TypeScript discriminated union can pattern-match on `kind`.
+#[derive(Debug, Clone, Serialize)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum UploadEntry {
+    Manga {
+        manga: Manga,
+        /// Mirrored from `manga.created_at` for ordering convenience;
+        /// the frontend reads this to display the timestamp in a
+        /// kind-agnostic column.
+        created_at: DateTime<Utc>,
+    },
+    Chapter {
+        manga_id: Uuid,
+        manga_title: String,
+        manga_cover_image_path: Option<String>,
+        chapter: Chapter,
+        created_at: DateTime<Utc>,
+    },
+}
+
+impl UploadEntry {
+    /// Timestamp used for chronological ordering. The repo sorts on
+    /// the underlying column server-side; this is here for callers
+    /// that need to merge or page in Rust.
+    pub fn created_at(&self) -> DateTime<Utc> {
+        match self {
+            UploadEntry::Manga { created_at, .. } => *created_at,
+            UploadEntry::Chapter { created_at, .. } => *created_at,
+        }
+    }
+}