feat: launcher script for running from a checkout without uv

Only click and cryptography are needed, both packaged by Arch, so a
plain ./boltcard-writer works when uv cannot be installed (Omarchy's
pinned mirror 404'd on the uv package during the first field test).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -26,8 +26,19 @@ uv run boltcard-writer readers
 ```
 
 `uv run` creates a virtualenv and installs the two Python dependencies on
-first use (needs internet once). With the ACR1252U plugged in you should see
-two readers, the starred one is used:
+first use (needs internet once).
+
+**No uv?** (e.g. the Omarchy mirror 404s on the package, try
+`sudo pacman -Syu uv` first). The only dependencies are click and
+cryptography, both in Arch's repos, and the checkout ships a launcher:
+
+```sh
+sudo pacman -S --needed python python-click python-cryptography
+./boltcard-writer readers        # instead of `uv run boltcard-writer readers`
+```
+
+With the ACR1252U plugged in you should see two readers, the starred one is
+used:
 
 ```
 * ACS ACR1252 1S CL Reader PICC 00 00