v2 release prep: installer, README, packaging, notes; retire the v1 scripts

Installer rewritten around a preflight: distro, package manager, display
manager, window manager, terminal, tmux, cargo, git, screen locker, touch
device, device permissions and free disk are all checked BEFORE anything is
installed, and the total cost is printed once for a single confirmation.
Prompts read /dev/tty so they still work when the script is piped from curl,
and fall back to defaults with a notice when there is no terminal at all.

Several "[ test ] && action" statements were set -e landmines: under set -e an
AND-OR list that ends up false aborts the script, so a box with no lightdm, no
i3 or nothing to install would have exited silently partway through detection
-- which is exactly the fresh-Debian case the installer exists for. Rewritten
as if-statements and verified against a stripped PATH with no tmux, cargo, git
or package manager present. Also fixed cargo detection reporting blank instead
of NOT INSTALLED: the status of `cargo --version | cut` is cut's, and cut
succeeds on empty input, so the fallback never fired.

Device access now defaults to a udev rule matching touchscreens only, rather
than the input group, which grants access to every input device including the
keyboard and needs a full logout.

README rewritten for someone who has not seen the project: what the photo
shows, the hardware, install, then a config built up step by step, each step
with the YAML and the resulting map. Every example is verified verbatim
against the binary, and every relative link resolves. The mechanism and the
reasoning move to notes/: DESIGN.md, HARDWARE-NOTES.md, V1-BASH.md, TODO.md.

cad/README.md was a verbatim copy of the one inside
geeekpi_rack_adapter_release_v1/, so every path in it -- including the
screenshot -- was broken from where it sits. Corrected to its own level, and
it now states once that the 9-inch screen, the 10-inch mini-rack mount and the
19-inch rack are three different measurements.

The v1 shell implementation is removed; it stays recoverable at tag v1.2 and
notes/V1-BASH.md carries the setting-by-setting migration table.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/config/coord.rs

@@ -48,9 +48,11 @@ impl std::str::FromStr for Coord {
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         let t = s.trim();
         // Split on the separator 'x', which cannot be part of either number.
-        let (row, col) = t
-            .split_once('x')
-            .ok_or_else(|| format!("{t:?} is not a coordinate -- expected \"<row>x<col>\", e.g. \"0x0\" or \"-1x0\""))?;
+        let (row, col) = t.split_once('x').ok_or_else(|| {
+            format!(
+                "{t:?} is not a coordinate -- expected \"<row>x<col>\", e.g. \"0x0\" or \"-1x0\""
+            )
+        })?;
         let parse = |part: &str, which: &str| -> Result<i32, String> {
             part.trim().parse::<i32>().map_err(|_| {
                 format!("{t:?} is not a coordinate -- the {which} {part:?} is not a whole number")
@@ -122,22 +124,43 @@ mod tests {
         assert_eq!(Coord::new(1, -2).window_name(), "r1cm2");
         for c in [Coord::new(0, 0), Coord::new(-1, -1), Coord::new(9, 9)] {
             let n = c.window_name();
-            assert!(!n.contains(':') && !n.contains('.') && !n.contains('-'), "{n}");
+            assert!(
+                !n.contains(':') && !n.contains('.') && !n.contains('-'),
+                "{n}"
+            );
         }
     }
 
     #[test]
     fn unquoted_hex_coordinate_gets_a_useful_error() {
         // This is what YAML actually hands us for `at: 0x0`.
-        let err = serde_yaml::from_str::<Coord>("0x0").unwrap_err().to_string();
+        let err = serde_yaml::from_str::<Coord>("0x0")
+            .unwrap_err()
+            .to_string();
         assert!(err.contains("hexadecimal"), "unhelpful error: {err}");
-        assert!(err.contains("at: \"0x0\""), "error should show the fix: {err}");
+        assert!(
+            err.contains("at: \"0x0\""),
+            "error should show the fix: {err}"
+        );
     }
 
     #[test]
     fn sorts_by_row_then_column() {
-        let mut v = vec![Coord::new(1, 0), Coord::new(-1, 5), Coord::new(0, 2), Coord::new(0, -1)];
+        let mut v = vec![
+            Coord::new(1, 0),
+            Coord::new(-1, 5),
+            Coord::new(0, 2),
+            Coord::new(0, -1),
+        ];
         v.sort();
-        assert_eq!(v, vec![Coord::new(-1, 5), Coord::new(0, -1), Coord::new(0, 2), Coord::new(1, 0)]);
+        assert_eq!(
+            v,
+            vec![
+                Coord::new(-1, 5),
+                Coord::new(0, -1),
+                Coord::new(0, 2),
+                Coord::new(1, 0)
+            ]
+        );
     }
 }