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.

.pi/skills/yellowjacket-dev/SKILL.md

@@ -195,6 +195,12 @@ Two rules about climbing:
 - **Do not write an e2e spec first.** Drive the flow by hand, then
   promote it with `/e2e`. Specs written blind assert on selectors that
   do not exist.
+- **Not every view has a nav item.** Since #25 the destinations are
+  configurable, Autotag is hidden by default and Downloads is absent
+  until a download client exists — so `getByTestId('nav-<view>')` waits
+  30 s for a locator that will never resolve. `navigateTo(page, view)`
+  (`e2e/support/fixtures.ts`) dispatches the app's own `navigate` event.
+  Click the nav item when the *nav* is what the spec is about.
 
 Before a commit, the gate is `make lint`, `make test`, `make ui-test`,
 `make bindings-check`, `make css-check` and — from `frontend/` —