feat(docker): Dockerfile for the Telegram host

Two-stage build, agent tools, Node 24, claude CLI, data dirs owned by app, DOTNET_EnableDiagnostics=0. Adds the MCP spec's deferred test that the Dockerfile's PLAYWRIGHT_MCP_VERSION equals PlaywrightPreset.DefaultPackage.

Spec change: the image keeps root as its user and the entrypoint drops to app with setpriv. With USER app, compose's docker-init (PID 1) runs as app and its /proc/1/environ exposes every secret to the agent's bash. The spec also lists the csprojs the restore layer copies (GoogleCalendar, Mcp, Scheduler included) and sets HOME=/home/app in the image.

.dockerignore

@@ -0,0 +1,17 @@
+**/bin
+**/obj
+**/TestResults
+**/*.user
+**/Properties/launchSettings.json
+.git
+.vs
+.idea
+.claude
+.volcanic
+.env
+.env.*
+tests
+samples
+docs
+*.md
+docker-compose.yml