Docs for strangers: real quick start, own-shelves guide, clone-safe stub guard

README rewritten for a fresh clone: working status, quick start with
env-var table and per-stage commands, photo-taking guidance, a
bring-your-own-shelves section (this repo carries the author's live
data), tokenless workflows, and a dev section. New committed
data/STUB_DATA.marker closes a real gap: the cache marker is
gitignored, so a fresh clone had stub-derived to_add.csv with no
guard — upload now refuses on either marker. Username docs: BGG_USERNAME
in .env is the one place it's needed; config.toml is a fallback.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/bggpipe/upload.py

@@ -415,14 +415,23 @@ def run_upload(
     rng = rng or random.Random()
     now = now or (lambda: datetime.now(UTC).isoformat(timespec="seconds"))
 
-    marker = cfg.cache_dir / "STUB_FIXTURES.marker"
-    if marker.exists():
+    # Two provenance markers guard the same fact from different angles: the
+    # cache marker travels with the stub XML (gitignored, so a fresh clone
+    # loses it), while data/STUB_DATA.marker is COMMITTED alongside the
+    # stub-derived CSVs — so a clone can never upload placeholder ids.
+    markers = [
+        cfg.cache_dir / "STUB_FIXTURES.marker",
+        cfg.data_dir / "STUB_DATA.marker",
+    ]
+    marker = next((m for m in markers if m.exists()), None)
+    if marker is not None:
         if not dry_run:
             typer.echo(
                 f"Refusing to upload: {marker} exists — every resolved "
                 "version_id is a synthetic stub placeholder. Once "
                 "BGG_API_TOKEN arrives: delete both cache dirs, re-record "
-                "fixtures, `resolve --force`, re-review, re-diff."
+                "fixtures, `resolve --force`, re-review, re-diff, then "
+                "delete the marker(s)."
             )
             raise typer.Exit(code=1)
         typer.echo(