docs: record what is still outstanding, and unstale the scanner section

Nothing here is broken — these are decisions not made and cleanups not done,
written down before the session's context is lost.

The two that can actually cost something: no daily stories run is scheduled,
and stories are the one surface that cannot be backfilled; and the `seeded`
flags in the state file were reconstructed by hand from a log rather than
derived from the archive DB, so losing artms.db without also clearing the
state file would leave those sources permanently unseeded and re-download
everything.

Also corrects "Scanner work (not done yet)", which shipped in 53b1f80 —
the three .json shapes are told apart structurally in gallery-dl-sidecar.ts
and isReel comes from the sidecar's type. That file lives on main: it parses
archives at display time and is viewer code, not tooling.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UXfdJu7QhSJLr47K7koTDF

docs/gallery-dl.md

@@ -560,18 +560,23 @@ Verify by asking gallery-dl's own interpreter, not the shell:
   has a dated twin. The scanner dedupes by index so they render once; it is
   wasted disk, not a display bug.
 
-## Scanner work (not done yet)
+## Scanner work — done
 
-`useArchiveScanner` currently treats any `.json` in the tree as a possible
-manifest. Adding gallery-dl sidecars needs it to distinguish three things:
+Shipped in `53b1f80` ("read gallery-dl sidecars for reel type and post dates").
+`useArchiveScanner` tells the three `.json` shapes apart **structurally**, not
+by filename, in `src/lib/gallery-dl-sidecar.ts`:
 
-1. Instagram export manifests (`posts_1.json`) — existing path.
-2. Instaloader `.json.xz` — existing path, GraphQL node shape.
-3. gallery-dl `.json` — new, flat shape, identified by having
-   `post_shortcode` + `type` at the top level.
+1. Instagram export manifests (`posts_1.json`) — top-level `media` array.
+2. Instaloader `.json.xz` — GraphQL node under `node` / `__typename`.
+3. gallery-dl `.json` — flat, `post_shortcode` + `type`, none of the above.
 
-Once (3) is read, `source`/`isStory` and the reel flag should come from `type`
-rather than from the directory and the lone-video heuristic.
+`post.isReel` now comes from the sidecar's `type`, which is Instagram's own
+classification, and beats every fallback in `post-tabs.ts`. Post dates are
+ranked rather than last-write-wins (`src/lib/post-dates.ts`): sidecar beats
+filename beats mtime.
+
+Note those files live on **`main`** — they parse the archive at display time
+and are viewer code, not fetching tooling.
 
 ## Test cases