[docs/packaging] add watcher crate, release artifacts, and smoke test

Author: taariq

docs/installers.md

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+# sqlite-watcher installation guide
+
+This document walks through running the sqlite-watcher service on Linux, macOS, and Windows. The watcher process should run beside the `.sqlite` file so it can tail the WAL and expose change batches over the embedded gRPC API.
+
+All platforms share these basics:
+
+- Create a token file (default `~/.seren/sqlite-watcher/token`) with restrictive permissions (owner read/write only).
+- Choose a queue database path (default `~/.seren/sqlite-watcher/changes.db`). Ensure the parent directory is `0700` on Unix.
+- Run `sqlite-watcher serve --queue-db <path> --listen <endpoint> --token-file <file>` to start the gRPC service. Endpoints use the `unix:/path` or `tcp:host:port` syntax.
+
+## Linux (systemd)
+
+1. Install binaries:
+
+   ```bash
+   sudo install -m 0755 database-replicator /usr/local/bin/database-replicator
+   sudo install -m 0755 sqlite-watcher /usr/local/bin/sqlite-watcher
+   ```
+
+2. Create token + queue directories:
+
+   ```bash
+   install -d -m 0700 ~/.seren/sqlite-watcher
+   openssl rand -hex 32 > ~/.seren/sqlite-watcher/token
+   ```
+
+3. Create `/etc/systemd/system/sqlite-watcher.service`:
+
+   ```ini
+   [Unit]
+   Description=sqlite-watcher for /srv/app.db
+   After=network-online.target
+
+   [Service]
+   User=replicator
+   ExecStart=/usr/local/bin/sqlite-watcher serve \
+     --queue-db /var/lib/sqlite-watcher/changes.db \
+     --listen unix:/run/sqlite-watcher.sock \
+     --token-file /home/replicator/.seren/sqlite-watcher/token
+   Restart=on-failure
+
+   [Install]
+   WantedBy=multi-user.target
+   ```
+
+4. Enable/start:
+
+   ```bash
+   sudo systemctl daemon-reload
+   sudo systemctl enable --now sqlite-watcher.service
+   ```
+
+## macOS (launchd)
+
+1. Copy binaries into `/usr/local/bin`.
+2. Save the following to `~/Library/LaunchAgents/com.seren.sqlite-watcher.plist`:
+
+   ```xml
+   <?xml version="1.0" encoding="UTF-8"?>
+   <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+   <plist version="1.0">
+   <dict>
+     <key>Label</key>
+     <string>com.seren.sqlite-watcher</string>
+     <key>ProgramArguments</key>
+     <array>
+       <string>/usr/local/bin/sqlite-watcher</string>
+       <string>serve</string>
+       <string>--queue-db</string>
+       <string>/Users/you/.seren/sqlite-watcher/changes.db</string>
+       <string>--listen</string>
+       <string>unix:/Users/you/.seren/sqlite-watcher/watcher.sock</string>
+       <string>--token-file</string>
+       <string>/Users/you/.seren/sqlite-watcher/token</string>
+     </array>
+     <key>RunAtLoad</key>
+     <true/>
+     <key>KeepAlive</key>
+     <true/>
+     <key>StandardOutPath</key>
+     <string>/Users/you/Library/Logs/sqlite-watcher.log</string>
+     <key>StandardErrorPath</key>
+     <string>/Users/you/Library/Logs/sqlite-watcher.log</string>
+   </dict>
+   </plist>
+   ```
+
+3. Load the agent: `launchctl load ~/Library/LaunchAgents/com.seren.sqlite-watcher.plist`.
+
+## Windows (Service)
+
+1. Copy `database-replicator.exe` and `sqlite-watcher.exe` to a directory on `%PATH%` (e.g. `C:\Program Files\Seren`).
+2. Create a token file under `%USERPROFILE%\.seren\sqlite-watcher\token`.
+3. Use the built-in `sc.exe` to install a service (or NSSM if you prefer a GUI):
+
+   ```powershell
+   sc.exe create sqlite-watcher binPath= "C:\Program Files\Seren\sqlite-watcher.exe serve --queue-db C:\data\sqlite-watcher\changes.db --listen tcp:127.0.0.1:6000 --token-file %USERPROFILE%\.seren\sqlite-watcher\token" start= auto
+   ```
+
+4. Start the service with `sc.exe start sqlite-watcher`.
+
+Remember to open the firewall only if the watcher must accept remote TCP connections. In most deployments, keep it bound to loopback or Unix sockets.
+
+## Running sync-sqlite on a schedule
+
+- Linux/macOS: use cron or systemd timers to run `database-replicator sync-sqlite ...` periodically.
+- Windows: create a Scheduled Task pointing at `database-replicator.exe sync-sqlite ...`.
+
+Consult the smoke test (`scripts/test-sqlite-delta.sh`) to see a minimal end-to-end example.