feat(mcp): stdio MCP server exposing the full API as tools

Add containr-mcp so MCP-compatible agents (Claude, Cursor, Devin)
operate the platform directly — ROADMAP2 phase A3. Reuses the CLI's
thin client and PAT auth; zero duplicated resource logic.

- ~60 containr_* tools across projects, services, deployments, logs,
  exec, variables, databases, cron, templates, nodes, scaling, ha,
  security, gateway, admin, notifications, tokens
- declarative tool specs → {param} path substitution, GET extras become
  query params, remaining args form the request body
- destructive tools require confirm:true and return isError without it
- results are pretty JSON; API error envelopes surface as isError
- configured via CONTAINR_API_URL + CONTAINR_TOKEN env; official
  modelcontextprotocol/go-sdk over StdioTransport

Verified over stdio: initialize + tools/list, auth_status returns the
token owner's identity, projects list, destructive refusal, token
creation through MCP.

Authored By: TDvorak <[email protected]>

docs/guides/CLI.md

@@ -69,3 +69,29 @@ containr up --project <id> --image ghcr.io/example/app:latest   # image, no buil
 
 Set `project_id` on the active profile to omit `--project` (stored in
 `~/.containr.yaml` under `profiles.<name>.project_id`).
+
+## MCP server
+
+`containr-mcp` (`go build ./cmd/mcp`) exposes the same API as MCP tools
+over stdio — every command group above maps to a `containr_*` tool
+(~60 tools). Destructive tools require the caller to pass
+`confirm: true`; results are pretty JSON with `isError` on failures.
+
+Client configuration (Claude Code, Cursor, Devin, any stdio MCP host):
+
+```json
+{
+  "mcpServers": {
+    "containr": {
+      "command": "containr-mcp",
+      "env": {
+        "CONTAINR_API_URL": "https://containr.example.com",
+        "CONTAINR_TOKEN": "cnp_..."
+      }
+    }
+  }
+}
+```
+
+Scope the token deliberately: `read` is enough for inspection agents,
+`write` for deploy automation, `admin` only for platform operations.