feat(backend): inject MCP servers in CLI passthrough mode per agent (#1158)

docs/add-agent-cli.md

@@ -141,6 +141,7 @@ Key implementation notes:
 - **`BuildCommand()`** returns the CLI command for structured protocol mode (the agent communicates via stdin/stdout with a protocol adapter). Include the protocol flag here (e.g. `--acp`, `--stream-json`).
 - **`Runtime()`** returns configuration used when running the agent in Docker or as a standalone process. Set `Protocol` to tell the adapter factory which transport to use.
 - **`IsInstalled()`** uses the `Detect()` helper with `WithFileExists()` to check for known installation paths. Set `SupportsMCP` and `MCPConfigPaths` on the result.
+- **MCP servers in passthrough** — set `MCPStrategy` on `PassthroughConfig` so the agent receives kandev's own tools server (plus any profile-configured MCP servers) when run in passthrough mode. Omitting it means **no MCP servers are injected in passthrough**. Pick the strategy that matches how your CLI loads MCP servers: `mcpconfig.ClaudeStrategy{}` (temp JSON file + `--mcp-config` flag), `mcpconfig.CodexStrategy{}` (repeated `-c mcp_servers.…` overrides), `mcpconfig.CursorStrategy{}` (project-local `.cursor/mcp.json`), or `mcpconfig.OpenCodeStrategy{}` (temp JSON + `OPENCODE_CONFIG` env var). To add a strategy for a CLI with a different mechanism, implement `mcpconfig.PassthroughMCPStrategy`. See ADR 0014 and `internal/agent/mcpconfig/passthrough.go`.
 - **`ListModels()`** can return a static list or dynamically query the CLI. Use `execAndParse()` from `helpers.go` for dynamic model discovery.
 - Use `Cmd()` builder for constructing commands fluently: `Cmd("myagent", "--flag").Model(...).Settings(...).Build()`.