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.svelte

@@ -18,6 +18,20 @@
     let { data } = $props();
     const manga = $derived(data.manga);
     const chapters = $derived(data.chapters);
+    const readProgress = $derived(data.readProgress);
+    /** Chapter row from the local chapters list when present (so we
+     *  can also surface the chapter title). Falls back below to the
+     *  server-supplied `chapter_number` when the chapter sits past
+     *  the first page of `chapters` (large mangas with >50 chapters). */
+    const continueChapter = $derived(
+        readProgress?.chapter_id
+            ? chapters.find((c) => c.id === readProgress.chapter_id) ?? null
+            : null
+    );
+    const continueChapterNumber = $derived(
+        continueChapter?.number ?? readProgress?.chapter_number ?? null
+    );
+    const continueChapterTitle = $derived(continueChapter?.title ?? null);
 
     const authors = $derived<AuthorRef[]>(manga.authors);
     const genres = $derived<GenreRef[]>(manga.genres);
@@ -328,6 +342,21 @@
 
     <section aria-label="chapters">
         <h2>Chapters</h2>
+        {#if continueChapterNumber != null}
+            <a
+                class="continue"
+                href="/manga/{manga.id}/chapter/{continueChapterNumber}"
+                data-testid="continue-reading"
+            >
+                <span class="continue-label">Continue reading</span>
+                <span class="continue-target">
+                    Chapter {continueChapterNumber}{#if continueChapterTitle}: {continueChapterTitle}{/if}
+                    {#if readProgress && readProgress.page > 1}
+                        — page {readProgress.page}
+                    {/if}
+                </span>
+            </a>
+        {/if}
         {#if chapters.length === 0}
             <p data-testid="chapters-empty">No chapters yet.</p>
         {:else}
@@ -536,6 +565,36 @@
         color: var(--text);
     }
 
+    .continue {
+        display: flex;
+        flex-direction: column;
+        gap: var(--space-1);
+        margin: var(--space-3) 0;
+        padding: var(--space-3);
+        background: var(--primary-soft-bg);
+        border: 1px solid var(--primary);
+        border-radius: var(--radius-md);
+        color: var(--text);
+        text-decoration: none;
+    }
+
+    .continue:hover {
+        background: var(--surface-elevated);
+        text-decoration: none;
+    }
+
+    .continue-label {
+        font-size: var(--font-xs);
+        color: var(--primary);
+        font-weight: var(--weight-semibold);
+        text-transform: uppercase;
+        letter-spacing: 0.04em;
+    }
+
+    .continue-target {
+        font-weight: var(--weight-medium);
+    }
+
     .chapter-list {
         padding-left: var(--space-6);
         color: var(--text);