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/migrations/0011_history.sql

@@ -0,0 +1,39 @@
+-- Per-user reading progress and uploader attribution.
+--
+-- Reading progress is the simplest shape that supports "jump to last
+-- read chapter" — one row per (user, manga). The reader writes
+-- through on chapter open and on page advance (debounced); the
+-- history view shows them sorted by most-recently-touched.
+--
+-- Uploader attribution adds nullable `uploaded_by` columns to the two
+-- upload sinks. Historical rows have NULL because the original
+-- handlers didn't track this; new uploads stamp the current user.
+
+CREATE TABLE read_progress (
+    user_id     uuid NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    manga_id    uuid NOT NULL REFERENCES mangas(id) ON DELETE CASCADE,
+    -- Chapter is nullable so a deleted chapter doesn't blow away
+    -- the user's progress row entirely — they just see "(chapter
+    -- removed)" in the history UI.
+    chapter_id  uuid REFERENCES chapters(id) ON DELETE SET NULL,
+    page        integer NOT NULL DEFAULT 1 CHECK (page >= 1),
+    updated_at  timestamptz NOT NULL DEFAULT now(),
+    PRIMARY KEY (user_id, manga_id)
+);
+
+-- Most queries on this table want "most recent first" per user; the
+-- composite index makes both filter and sort index-only.
+CREATE INDEX read_progress_user_idx
+    ON read_progress (user_id, updated_at DESC);
+
+ALTER TABLE mangas
+    ADD COLUMN uploaded_by uuid REFERENCES users(id) ON DELETE SET NULL;
+CREATE INDEX mangas_uploaded_by_idx
+    ON mangas (uploaded_by, created_at DESC)
+    WHERE uploaded_by IS NOT NULL;
+
+ALTER TABLE chapters
+    ADD COLUMN uploaded_by uuid REFERENCES users(id) ON DELETE SET NULL;
+CREATE INDEX chapters_uploaded_by_idx
+    ON chapters (uploaded_by, created_at DESC)
+    WHERE uploaded_by IS NOT NULL;