Starling 0.2.2 — the Text Editor ships, and windows resize properly

A fix release: the Text Editor that 0.2.1 promised but never shipped, window
resizing that apps actually follow, and a yellow debug bar that no user should
ever have seen.

The dock advertised a Text Editor that was not there (#4)

0.2.1's dock showed a Text Editor icon at slot 4 — and clicking it did
nothing, because the binary was never in the package. The app has existed all
along (a plain-text editor with formatting, font sizing and Open/Save); the
packager carried its own hand-maintained list of apps, and the catalog had
outgrown it by two: Text Editor and Image Viewer were built by every test
tier, staged, and then left out of the .deb. From a user's seat there simply
was no text editor, so "Add native Text Editor app" was exactly the right bug
report — thanks @AsciiWolf.

The packaged app set is now derived from the registry, the same single source
the dock and the launcher already read, and a declared app with no binary
fails the build instead of shipping silently. Both apps are in 0.2.2.

Windows now resize their contents

Shrinking a window did not reflow the app inside it: the Terminal kept its
launch-time grid (and its pty kept the launch-time dimensions, so stty size
lied), and once the mismatch got big enough a solid yellow
"BOTTOM OVERFLOWED BY n PIXELS" bar was painted over the app — a Flutter
developer diagnostic that upstream strips from release builds, and this port
did not.

Three fixes land together: the overflow indicator is debug-only again, the
framework rebuilds the widget tree when the window metrics change (this port
has no MediaQuery, so nothing else told an app its size changed), and
first-party apps ship against one shared framework build instead of nine
private copies of it.

The power menu is now tested the way you would use it

New in the release gate: the packaged desktop is shut down through its own
power menu — icon, Shut Down…, confirm — and the pass requires the machine to
actually reach poweroff, on the seat-active session logind authorises. Restart
and Log Out were verified the same way. (The menu itself shipped in 0.2.1 as
the only way to power off from the UI; until now nothing exercised it.)

Also in this release

• The three power-menu confirm panels (Shut Down / Restart / Log Out) now
  share identical geometry. Log Out's prompt used to wrap to a second line,
  which pushed its buttons ~33px below the other two — a destructive button
  should never move between near-identical dialogs.
• The engine scans out the connector's preferred mode instead of the
  biggest one it advertises — kinder to virtual displays whose largest mode
  outruns their VRAM, and to panels whose EDID knows best.
• starling_0.2.2-2_amd64.deb below is the byte-identical artifact the
  release gate passed: clean-machine install, GDM login, seat-active polkit
  checks, the functional suite with a GPU and with none, and the power-menu
  shutdown.

Install as before: docs/INSTALL.md.