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>

frontend/src/routes/manga/[id]/+page.ts

@@ -1,15 +1,23 @@
 import { getManga } from '$lib/api/mangas';
 import { listChapters } from '$lib/api/chapters';
 import { listMyBookmarksOrEmpty } from '$lib/api/bookmarks';
+import { getMyReadProgressForManga } from '$lib/api/read_progress';
 import type { PageLoad } from './$types';
 
 export const ssr = false;
 
 export const load: PageLoad = async ({ params }) => {
-    const [manga, chapters, bookmarks] = await Promise.all([
+    const [manga, chapters, bookmarks, readProgress] = await Promise.all([
         getManga(params.id),
         listChapters(params.id),
-        listMyBookmarksOrEmpty()
+        listMyBookmarksOrEmpty(),
+        // Null when guest or never-read — page handles both cases.
+        getMyReadProgressForManga(params.id)
     ]);
-    return { manga, chapters: chapters.items, bookmarks: bookmarks.items };
+    return {
+        manga,
+        chapters: chapters.items,
+        bookmarks: bookmarks.items,
+        readProgress
+    };
 };