docs: record standalone deployment session

docs/changelog.md

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+# Changelog
+
+## 2026-07-19
+
+### Standalone installation and deployment
+
+- Added `rsmon-worker install` for installing the current binary, a mode-0600
+  environment file, and a root-owned systemd service.
+- Added `rsmon-worker deploy` for installing workers over SSH with key or
+  password authentication, optional secret files, and host-key verification
+  through `known_hosts` or a pinned fingerprint.
+- Added `--token-file`, `--url`, `--api-key`, and `--no-start` deployment
+  options.
+- Added optional `--docker` deployment using the prebuilt
+  `reg.rsxx.ru/rsmon/rsmon-worker:latest` image. Remote Docker deployment pulls
+  the image on the target host and does not depend on the local architecture.
+- Simplified the default systemd service to `Type=simple`, `User=root`, and
+  `Restart=on-failure`.
+- Reworked the legacy `scripts/install-systemd.sh` script as a compatibility
+  wrapper around the built-in installer.
+
+### Standalone repository cleanup
+
+- Removed the remaining certificate-bundle fallback under `/data/rsmon` and
+  updated its documentation.
+- Changed Docker build and runtime bases to public Go and Debian images.
+- Documented binary, systemd, Docker, and SSH deployment workflows.
+- Added installer and SSH host-verification tests.
+
+### Verification
+
+- Passed `make test`, `make build`, `go vet`, and `go mod verify`.
+- Validated systemd units, Compose configuration, Docker image pull and
+  execution, and production worker job reporting.
+- Published the changes as commit `3256dcd` (`feat: add worker install and
+  deploy`) on `master`, triggering the Docker image workflow.