Replace the landing copy with the recently opened documents

[andiwand]

🤖 Generated with Claude Code

Third of six, stacked. Base: landing/02-material3 (#524). This is the one that changes what people see.

The app opened on a static welcome screen — a title and three icon rows explaining that it can view, search and edit documents, none of it actionable. The recently opened list already existed but was buried as the last row of the file manager chooser, so almost nobody found it.

The landing screen is now that list, with an empty state on first run.

LandingFragment is a sibling of DocumentFragment, state in a ViewModel so it survives the recreation a rotation or dark-mode toggle causes; MainActivity keeps only the container swap it already did.

• RecyclerView and the two lifecycle artifacts already arrived through material, so declaring them costs no apk size — it only stops a material bump from silently taking a compile dependency away.
• No coroutines. They are on the classpath transitively via the play libraries and nothing here is written in them, so the list loads on an executor and publishes through LiveData, like the loaders.
• setLandingVisible is not ceremony. The fragment is hidden rather than stopped when a document opens, so nothing in the lifecycle fires when one is closed — without it the list would miss the document just added to it.

The catch-all switch keeps its place under a settings header; it is exactly the setting a stuck user has to find. Its logic moves to CatchAllSetting, but applyOnLaunch stays in MainActivity.onCreate — the upgrade re-toggle has to run even when the app is launched straight into a document.

Retires landing_intro_* and the size-qualified styles.xml files that existed only for the old layout.

Verification

Unit, lint and 16 instrumented tests green, including four new landing tests.