feat: add npm nightly release channel (#2126)

README.md

@@ -148,6 +148,23 @@ kandev
 - `npx kandev@latest` (always uses the latest published version)
 - `npm install -g kandev@latest`
 
+To try the current prerelease from `main`, use npm's `nightly` tag:
+
+```bash
+npx -y kandev@nightly
+# or
+npm install -g kandev@nightly
+```
+
+`npx` runs a transient Nightly without changing a global package. The global install replaces your
+installed Kandev until you reinstall `kandev@latest`.
+
+Nightlies are best-effort builds scheduled for 12:00 UTC when `main` has changed since the latest
+stable release. They do not move `latest`, and no Homebrew or Desktop nightly channel is published.
+A verified Kandev-managed npm/npx user service can switch between Stable and Nightly in
+**Settings > System > Updates**. Other install types expose only Stable in that page; npm/npx users
+can still invoke `@nightly` directly with the commands above.
+
 The worktrees and sqlite db live in `~/.kandev` by default. Works on macOS, Linux, and Windows (WSL or native).
 
 ### From Source