Release 0.2.0

Minor, not patch: colours and sizing move into a config file and the grid
scrolls, so behaviour people could depend on has changed shape.

- ~/.config/wl-pick/config sets colours, border, thumbnail size and the
  flags, as flat `key = value` lines; a flag still beats the file.
- Sizes take sway's units. 70ppt is a percentage of the display the grid
  appears on, resolved per run, so one config suits monitors of different
  sizes. The overlay maps on the focused display explicitly, at that
  display's scale, rather than taking the largest scale in use.
- Give only tile-width and the height follows the display's aspect, which
  is roughly the shape of the windows on it.
- More rows than fit now scroll, with a scrollbar, PgUp/PgDn, and the
  selection always revealed. Tiles out of view are unmapped and skipped
  by live capture.

Also corrects rust-version, which said 1.88 while cosmic-text has needed
1.89 all along: cargo was resolving 0.1.1 against a floor its own
dependency could not meet, and said so if you looked. It now locks
cleanly.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "wl-pick"
-version = "0.1.1"
+version = "0.2.0"
 edition = "2024"
 description = "A live grid of window and display previews, for picking one"
 license = "MIT"
@@ -8,8 +8,8 @@ repository = "https://github.com/mil-ad/wl-pick"
 readme = "README.md"
 keywords = ["wayland", "sway", "wlroots", "screencast", "switcher"]
 categories = ["command-line-utilities", "os::unix-apis"]
-# let-chains, which are edition 2024 and stable from here on
-rust-version = "1.88"
+# The floor is cosmic-text, which needs 1.89; let-chains here need 1.88.
+rust-version = "1.89"
 
 [dependencies]
 wayland-client = "0.31"