docs: record that destinations are configuration

Beside the three navigation paragraphs, since it is the fourth thing
the shell states about where the user can go.

Two notes are measured facts rather than design: a default expressed as
an *absent key* survives an existing seed, where one expressed as a zero
value does not; and a spec can no longer assume a destination has a nav
item.

CLAUDE.md

@@ -1032,6 +1032,71 @@ whole way through — so it was green on the broken build. Same trap as
 `layout-overflow.spec.ts` and `page-header`: a spec named for the
 behaviour, measuring the plumbing.
 
+**Which destinations exist is configuration, and hiding one takes away
+the nav item and nothing else.** Eleven sidebar entries is more than
+most libraries need (#25), so each is toggleable from Settings →
+Navigation, Autotag is off until asked for, and Downloads is absent
+until there is a client to download with — a destination for a feature
+that cannot work is worse than none. `navigate` still resolves a hidden
+view, which is not a nicety: detail views navigate into these and the
+launch page is one of them. Nothing needed a special case for the
+highlight either, because the paragraph above moved that onto
+`active-view-store`: the sidebar asks `isActive(id)` per *rendered*
+item, so a hidden view lights nothing exactly as a detail view does.
+
+Five things about it are load-bearing.
+
+**The stored shape is a map keyed by view id, and an absent key means
+that view's own default** (`backend/config.Views`). That is what makes
+this need no migration in either direction, and it is the polarity rule
+`AllowMeteredCatalogDownload` states: the zero value is the intended
+answer. A `HiddenViews []string` cannot express "Autotag off by
+default" at all — its zero value is *hide nothing* — and a struct with
+a boolean per view turns a view that later stops existing into stored
+garbage. Here an unknown key is dropped on load and a view added later
+gets its own default rather than being invisible or forcibly visible.
+It is also what makes #73's `#25 → #27` order safe rather than
+backwards: when Jobs folds into Settings, `jobs = true` in somebody's
+config is a key nothing asks about.
+
+**Two states the user could not get out of are refused, in the config
+and not in the checkbox.** Settings is never hideable and the launch
+page is not hideable while it is the launch page. `config.toml` is
+hand-editable, so a disabled checkbox is the affordance and
+`SetViewVisible` is the rule — an app that can be locked out of its own
+Settings by a typo in TOML is a support problem nobody can debug
+remotely. On *load* the launch page is instead un-hidden rather than
+refused: there is nobody to tell, and the honest reading of "my launch
+page is Autotag" is that this user wants Autotag, not that their launch
+page should be silently reset to something they did not choose.
+
+**Downloads is gated at the nav and not in the config**, on
+`downloadStore.available`, so switching it on in Settings still means
+what it says once a client exists and the tab appears without a restart
+(#37's rule). `available` is false until the providers have loaded,
+which makes the item *appear* on a fresh launch rather than appearing
+and then vanishing.
+
+**The tab bar honours the toggles too, and the reason is local rather
+than a general rule about phones.** `PHONE_COLUMN_IDS` is the precedent
+for "what a phone shows is a different question", and it would apply —
+except that `bottom-nav`'s "More" opens the *same* `<app-sidebar>`,
+which filters, so an unfiltered bar would contradict its own drawer one
+tap away. Which four tabs is still plan 016's committed subset; this
+only removes from it, and "More" is never filtered because it is how
+everything else stays reachable.
+
+**The list of destinations is `services/view-meta.ts`**, on
+`shortcut-meta.ts`'s pattern, because #25 gave it a second reader:
+Settings renders a toggle per view and needs the same labels in the
+same order. Which views exist and what an unconfigured install shows is
+Go's (`backend/config.Views`, which `DefaultPage`'s validation reads
+too, so the launchable set is not a second list); how they are *drawn*
+is the frontend's, beside the rest of the icon vocabulary. The binding
+returns the **resolved** map for every view, so the frontend holds no
+copy of the defaults — which would be the copy that shipped in the
+binary rather than the one being edited.
+
 **A primary view is cached, not unmounted.** `index.ts` keeps every
 primary view in the DOM and toggles a `.view-hidden` class, because that
 is what preserves `scrollTop` across navigation — so