feat(maestro): add install.sh bootstrap for one-line install/update

Single command for both first install and subsequent updates:

  curl -sSf https://git.naps.pt/naps62/maestro/raw/branch/main/install.sh | sh

Builds `maestro-installer` into a temp `--root`, runs the wizard, cleans up —
so only `maestrod` and `maestro` persist in `~/.cargo/bin`. Re-running updates
in place via cargo install's overwrite semantics. Wizard flags pass through
with `sh -s --`. Docs updated to lead with the one-liner.

Refs NAP-225.

docs/INSTALL.md

@@ -1,11 +1,19 @@
 # Installing Maestro
 
-The fastest way to get `maestrod` (per-host daemon) and `maestro` (CLI) onto a
-host is the install wizard:
+One command, used for both first install and subsequent updates:
 
 ```sh
-cargo install --git https://git.naps.pt/naps62/maestro maestro-installer
-maestro-install
+curl -sSf https://git.naps.pt/naps62/maestro/raw/branch/main/install.sh | sh
+```
+
+The bootstrap script builds `maestro-installer` into a temp directory, runs the
+wizard, and cleans up — only `maestrod` and `maestro` end up persisted in
+`~/.cargo/bin`. Re-run any time to update; `cargo install` overwrites in place.
+
+Pass flags through to the wizard via `sh -s --`:
+
+```sh
+curl -sSf https://git.naps.pt/naps62/maestro/raw/branch/main/install.sh | sh -s -- --yes --no-systemd
 ```
 
 The wizard:
@@ -60,7 +68,19 @@ systemctl --user status maestrod
 journalctl --user -u maestrod -f
 ```
 
-## Manual install (no wizard)
+## Running the wizard without the bootstrap script
+
+If you'd rather not pipe a script:
+
+```sh
+cargo install --git https://git.naps.pt/naps62/maestro maestro-installer
+maestro-install
+```
+
+This leaves `maestro-installer` permanently in `~/.cargo/bin` — the bootstrap
+script avoids that by installing to a scratch dir.
+
+## Fully manual install (no wizard)
 
 ```sh
 cargo install --git https://git.naps.pt/naps62/maestro --locked maestro-daemon