fix: address code review on #27

- The empty state is about an empty library, not a brand-new Reader:
  listView.Fresh becomes EmptyLibrary and moves behind the tab-specific
  branches, so "No favourites yet" is no longer shadowed for a Reader whose
  library happens to be empty. The action key stays put — hiding it was
  never asked for.
- The owner is not a revocable Reader: their row offers no button and
  POST /readers/{owner}/revoke is a 404, so the one row where the control
  would sign out the tapping browser cannot be reached by a hand-rolled
  POST either.
- Modify isolation is asserted in both directions, and the owner's own
  sign-in through the OAuth callback is pinned to the seeded row.
- CUTOVER.md and REDEPLOY.md still grepped API_TOKEN out of .env for their
  smoke tests, which the last commit deleted; both now take the acting
  Reader's derived credential.
- Roster type follows the machine-fact spec (500 10-11px mono, tracked),
  and PRODUCT.md names the Readers panel instead of claiming there is no
  owner surface at all.

CUTOVER.md

@@ -271,7 +271,10 @@ would catch a correct import behind a broken join:
 
 ```bash
 API=https://bookmark-api.violetcrown.my.id
-TOKEN=$(grep -E '^API_TOKEN=' .env | cut -d= -f2)   # grace-window credential
+# Your own Reader credential: sign in to the web UI and take it from the
+# Userscripts panel's install link, or read the API_TOKEN constant out of an
+# already-installed script. There is no credential in .env to grep.
+TOKEN=<your Reader credential>
 curl -s -H "Authorization: Bearer $TOKEN" $API/bookmarks |
   python3 -c 'import json,sys; print(len(json.load(sys.stdin)))'   # -> 29
 ```