feat(keys): Back returns focus to the item a view was opened from; "Feed" everywhere; every backend id named

Owner answers to the E11 S5 raises (2026-09-13): 1 → A, 2 → "Feed" in every language, 3 → translate the
proxy label and fix every config key missing in BOTH languages ("maintenance", "tmdb" — old bugs).

Focus across a view change (1-A). Opening a Plex title from Home's rail, a channel from the Channels
table or a title from a Plex grid switches the page or the sub-view, which unmounts the list; Back used
to hand focus to <body>, so the next `j` started over at the top. The YouTube player (an overlay)
already restored onto the card.
- `lib/listNav`: `navPosition()` (list's place in reading order, the page's list count, item index)
  and `restoreNavPosition()`: focuses the item once the page has as many lists on screen as when it was
  left, polls on a timer (a hidden tab runs no animation frames), gives up after 2 s or at once when
  something already holds focus, focuses without scrolling (the scroll restore owns the position).
- `lib/history`: `rememberNavPosition()` stamps `sfNav` onto the entry being left and returns the state
  without it (a new entry must not inherit it); one popstate listener restores and spends the stamp,
  so a later landing on the same entry (an overlay closing over it) cannot pull focus to an old item.
- Called before every view push: `setPage`, `openChannel`, `enterYtSearch`, `useHistorySubview.open`,
  the Channels tab push. `navPosition.wiring.contract.test` fails on any `history.pushState(` without
  it (the overlay stack's own push is the one exemption).

"Feed" (2). The module is "Feed" in both languages: every "hírfolyam" in the Hungarian UI (≈45 strings,
suffixed: Feedből, Feeded, Feedben…) and the prose "feed" in English that means the module ("your
Feed", "Hide from Feed"); "RSS feed" keeps its meaning. The welcome email says it too.

Backend ids without a name (3). The Configuration page showed `maintenance`, `tmdb`,
`maintenance_revalidate_batch`, `download_upload_max_bytes`, `audit_retention_days`, `plex_overlay_map`,
`tmdb_api_key` and `tmdb_language` as raw identifiers — the lookup falls back to the id, and the i18n
parity test stayed green because both languages missed the same keys. Added labels + hints (EN/HU),
the two groups (and their tab order), the missing `scheduler.jobDesc.demo_reset`, removed the stale
`plex_sync_interval_min` field, and "YouTube API kimenő proxy". `i18n/backendIds.contract.test` reads
`sysconfig.SPECS`, `scheduler.JOB_INTERVALS` and the audit/quota action enums from the backend sources
and fails on an id without its name in either language, or a name left for an id the backend dropped.

backend/app/mailtext.py

@@ -175,7 +175,7 @@ MAIL_TEXT: dict[str, dict[str, str]] = {
         "en": (
             "Hi,\n\n"
             "Someone has opened up Siftlode for you — a quiet, self-hosted reader for your YouTube "
-            "subscriptions. Every upload from the channels you follow lands in one feed you can "
+            "subscriptions. Every upload from the channels you follow lands in one Feed you can "
             "actually filter and sort, with no algorithm deciding what you see, and no Shorts or "
             "livestreams unless you want them.\n\n"
             "{next_step}\n\n"
@@ -186,7 +186,7 @@ MAIL_TEXT: dict[str, dict[str, str]] = {
             "Szia,\n\n"
             "Valaki megnyitotta előtted a Siftlode-ot — ez egy csendes, saját üzemeltetésű olvasó "
             "a YouTube-feliratkozásaidhoz. A követett csatornák minden feltöltése egyetlen "
-            "hírfolyamba érkezik, amit tényleg tudsz szűrni és rendezni; nincs algoritmus, ami "
+            "Feedbe érkezik, amit tényleg tudsz szűrni és rendezni; nincs algoritmus, ami "
             "eldönti, mit látsz, és nincs Shorts vagy élő adás, hacsak nem kéred.\n\n"
             "{next_step}\n\n"
             "Nem sürget semmi — az ajtó nyitva marad.\n\n"