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>

cad/README.md

@@ -2,9 +2,13 @@
 
 A pair of side adapters for mounting the **GeeekPi 9-inch 1280x720 3U rack-mount touchscreen monitor** in a standard **19-inch equipment rack**.
 
+Three sizes get mentioned here and they are three different things: the **screen**
+is 9 inches, the mount it ships for is the **10-inch mini-rack** standard, and
+these adapters convert that to a **19-inch** equipment rack.
+
 The design also provides **three keystone-jack positions on each side of the display**.
 
-![Installed adapter](docs/installed.jpg)
+![Installed adapter](geeekpi_rack_adapter_release_v1/docs/installed.jpg)
 
 ## Release v1
 
@@ -18,22 +22,26 @@ The mounting geometry has been physically tested in a standard 19-inch rack.
 ## Files
 
 ```text
-.
-├── README.md
-├── 3d-print/
-│   ├── geeekpi_19in_adapter_LEFT_release-v1.stl
-│   ├── geeekpi_19in_adapter_RIGHT_release-v1.stl
-│   ├── geeekpi_19in_adapter_LEFT_release-v1_AnycubicMegaPro.gcode
-│   └── geeekpi_19in_adapter_RIGHT_release-v1_AnycubicMegaPro.gcode
-├── sendcutsend/
-│   ├── geeekpi_19in_adapter_LEFT_release-v1.dxf
-│   └── geeekpi_19in_adapter_RIGHT_release-v1.dxf
-├── source/
-│   └── geeekpi_19in_adapter_release-v1.scad
-└── docs/
-    └── installed.jpg
+cad/
+├── README.md                              this file
+├── geeekpi_rack_adapter_release_v1/       <- use this one
+│   ├── 3d-print/
+│   │   ├── geeekpi_19in_adapter_LEFT_release-v1.stl
+│   │   ├── geeekpi_19in_adapter_RIGHT_release-v1.stl
+│   │   ├── geeekpi_19in_adapter_LEFT_release-v1_AnycubicMegaPro.gcode
+│   │   └── geeekpi_19in_adapter_RIGHT_release-v1_AnycubicMegaPro.gcode
+│   ├── sendcutsend/
+│   │   ├── geeekpi_19in_adapter_LEFT_release-v1.dxf
+│   │   └── geeekpi_19in_adapter_RIGHT_release-v1.dxf
+│   ├── source/
+│   │   └── geeekpi_19in_adapter_release-v1.scad
+│   └── docs/
+│       └── installed.jpg
+└── geeekpi_v25_FINAL_candidate_package/   earlier candidate, superseded by v1
 ```
 
+Paths below are relative to `geeekpi_rack_adapter_release_v1/`.
+
 ## Key dimensions
 
 | Feature | Dimension |
@@ -70,7 +78,8 @@ Good bed leveling matters a lot for these parts because they are broad and very
 
 ## SendCutSend / metal version
 
-The `sendcutsend/` directory contains separate left and right DXF files.
+The `geeekpi_rack_adapter_release_v1/sendcutsend/` directory contains separate
+left and right DXF files.
 
 A good configuration for the metal adapters is:
 
@@ -98,7 +107,8 @@ Depending on the rack, display, and door clearance, small spacers or standoffs b
 
 ## Editing the design
 
-The editable OpenSCAD source is in `source/`.
+The editable OpenSCAD source is in
+`geeekpi_rack_adapter_release_v1/source/`.
 
 To generate a side, change:
 
@@ -108,7 +118,8 @@ side = "left";
 
 to either `"left"` or `"right"`, then render/export the STL.
 
-The DXF files in `sendcutsend/` are the intended files for sheet-metal cutting.
+The DXF files in `geeekpi_rack_adapter_release_v1/sendcutsend/` are the intended
+files for sheet-metal cutting.
 
 ## Notes