feat(maestro): installer drops optional maestro-web systemd unit (NAP-249)

New helpers in maestro-installer::systemd:

* `render_web_unit` — same shape as the daemon unit, ordered after
  `maestrod.service` so the proxy doesn't 502 on startup.
* `user_web_unit_path` / `default_maestro_web_path` — under `~/.config/`
  and `~/.cargo/bin/` respectively.

New wizard step (NAP-241 deferred this; phone-dogfood on 2026-05-26
surfaced it): after the daemon+systemd flow, optionally
`cargo install maestro-web` and lay down
`~/.config/systemd/user/maestro-web.service`. Re-runs detect the existing
unit and refresh + restart silently.

New flags:

* `--no-web` — skip the prompt entirely (headless hosts).
* `--web-exec-start <path>` — override the unit's ExecStart.

Non-interactive (`--yes` / piped) skips the web step unless an existing
unit is being refreshed — operators opt in by re-running once
interactively, then subsequent unattended re-runs refresh automatically.

docs/INSTALL.md updated with the new flow + flags.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/INSTALL.md

@@ -51,26 +51,48 @@ Both binaries land in `~/.cargo/bin` — make sure that's on your `$PATH`.
 ## Adding the browser UI (optional)
 
 `maestro-web` is a separate binary that serves the SPA bundle and reverse-
-proxies API calls to a co-located `maestrod`. Install it where you want a
-browser UI:
+proxies API calls to a co-located `maestrod`.
+
+**Interactive install (default path).** The wizard now offers it as an
+optional step right after the daemon flow:
+
+```text
+Optional: install the browser UI (`maestro-web`)?
+Install maestro-web? [Y/n]
+```
+
+Press `Y` and it `cargo install`s `maestro-web`, drops a
+`~/.config/systemd/user/maestro-web.service` unit (ordered after
+`maestrod.service`), reloads systemd, and offers to enable + start it. Re-runs
+of `./install.sh` detect the existing unit and refresh + restart silently.
+
+Pass `--no-web` to skip the prompt entirely (headless hosts), or `--yes`
+with `--no-web` for non-interactive daemon-only installs. (Bare `--yes`
+without `--no-web` *skips* the web step too — opt in by re-running once
+interactively.)
+
+**Frontend build prerequisite.** `maestro-web` embeds the SPA bundle at
+compile time, so before running the installer:
 
 ```sh
 pnpm -C web install --frozen-lockfile
 pnpm -C web build
-cargo install --git https://git.naps.pt/naps62/maestro --locked maestro-web
 ```
 
-…or, from a checkout, `just web` then `cargo install --path crates/maestro-web --locked`.
+Or `just web` from a workspace checkout.
 
-It defaults to binding `127.0.0.1:8080` and proxying to `http://127.0.0.1:7070`
-(the daemon's default `bind_addr`). The `[web]` section of
+**Defaults.** `bind_addr = 127.0.0.1:8080`, `daemon_url =
+http://127.0.0.1:7070`. The `[web]` section of
 `~/.config/maestro/config.toml` overrides both — see
-`crates/maestro-web/README.md`. **Trust model:** anyone who can reach the bind
-address can use it; pick `127.0.0.1` for local-only, a WireGuard/LAN address
-for one-segment access, never a public IP without adding auth first.
+`crates/maestro-web/README.md`.
 
-Headless hosts (servers, dev VMs) install only `maestrod`. Hosts where you
-want browser access install both.
+**Trust model.** Anyone who can reach the bind address can use it. Pick
+`127.0.0.1` for local-only, a WireGuard/LAN address for one-segment access,
+never a public IP without adding auth first.
+
+Headless hosts (servers, dev VMs) skip the prompt with `--no-web`. Hosts
+where you want browser access answer yes — both binaries end up in
+`~/.cargo/bin`.
 
 ## Flags
 
@@ -83,7 +105,9 @@ want browser access install both.
 | `--exec-start <path>` | Override the systemd unit's `ExecStart` (default `~/.cargo/bin/maestrod`). |
 | `--no-systemd` | Skip the systemd step even if detected. |
 | `--no-configure` | Skip the `maestrod configure` step. |
-| `-y`, `--yes` | Non-interactive: install binaries + drop systemd unit + reload + enable, but **don't** auto-run `configure` or auto-start the unit (those need real config). |
+| `--no-web` | Skip the optional `maestro-web` install step. |
+| `--web-exec-start <path>` | Override the web unit's `ExecStart` (default `~/.cargo/bin/maestro-web`). |
+| `-y`, `--yes` | Non-interactive: install binaries + drop systemd unit + reload + enable, but **don't** auto-run `configure` or auto-start the unit (those need real config). Also skips the web step unless an existing `maestro-web.service` is being refreshed. |
 
 ## What the systemd unit looks like