docs: publish Tend Compose continuity evidence

Export the reviewed allowlisted snapshot from private source commit 07c1655921f21ee5e4fc4d85639d199e8867b17d. This records the Docker Compose activation, schema-compatible rollback, and stateful migration resource findings from Observatory Preview 19 dogfooding.

AI-Assisted: OpenAI Codex
Signed-off-by: Cole Speelman <crspeelman@gmail.com>

examples/blue-green/caddy-handler.template

@@ -0,0 +1,2 @@
+# Managed by Tend. The enclosing site and route matchers remain operator-owned.
+reverse_proxy {{UPSTREAM}}

examples/blue-green/example-site@.service

@@ -0,0 +1,18 @@
+[Unit]
+Description=Example site (%i)
+After=network.target
+
+[Service]
+Type=simple
+DynamicUser=yes
+ExecStart=/opt/example-site/slots/%i/example-site
+EnvironmentFile=/etc/tend/environment/example-site.env
+EnvironmentFile=/etc/tend/slots/example-site-%i.env
+NoNewPrivileges=yes
+PrivateTmp=yes
+ProtectSystem=strict
+ProtectHome=yes
+Restart=on-failure
+
+[Install]
+WantedBy=multi-user.target

examples/blue-green/tend.json

@@ -0,0 +1,26 @@
+{
+  "schema_version": 2,
+  "service": { "name": "example-site", "allowed_host": "example.test", "environment_file": "/etc/tend/environment/example-site.env" },
+  "build": { "package": "./cmd/site", "binary": "example-site", "branch": "main" },
+  "deployment": {
+    "strategy": "blue_green",
+    "root": "/opt/example-site",
+    "lock_file": "/run/lock/tend-deploy.lock",
+    "state_file": "/opt/example-site/tend-state.json",
+    "event_log": "/opt/example-site/deployment-events.jsonl",
+    "health_path": "/healthz",
+    "readiness_path": "/readyz",
+    "candidate_timeout_seconds": 30,
+    "activation_window_seconds": 10,
+    "smoke": [{ "path": "/", "contains": "Example site" }],
+    "public_smoke": [{ "url": "https://example.test/", "contains": "Example site" }],
+    "blue_green": {
+      "caddy_config": "/etc/caddy/Caddyfile",
+      "caddy_handler": "/etc/caddy/example-site-handler.caddy",
+      "caddy_handler_template": "/etc/example-site/caddy-handler.template",
+      "bootstrap_active": "blue",
+      "blue": { "unit": "example-site-blue.service", "address": "127.0.0.1:8090", "link": "/opt/example-site/slots/blue" },
+      "green": { "unit": "example-site-green.service", "address": "127.0.0.1:8091", "link": "/opt/example-site/slots/green" }
+    }
+  }
+}