feat(devenv): add containerized development environment (#116)

* feat(devenv): add containerized development environment

Replace local-process dev workflow with a fully containerized stack
using docker compose. This enables consistent development across
machines without requiring local Go/Node toolchains or containerd.

- Add Dockerfile.server.dev with containerd + CNI networking support
- Add Dockerfile.web.dev for frontend dev server
- Add server-dev-entrypoint.sh for containerd lifecycle management
- Expand devenv/docker-compose.yml with server, agent, web, migrate
  and deps services with proper health checks and dependency ordering
- Update app.dev.toml to use container service names instead of localhost
- Refactor mise.toml dev tasks to drive docker compose workflow
- Support agent_gateway.server_addr in config package for inter-container
  communication

* feat(devenv): add hot-reload and registry mirror support

- Add air for Go server hot-reload in dev containers
- Fix agent_gateway host in dev config (0.0.0.0 -> agent)
- Add configurable registry mirror for China mainland users
- Unify MCP image refs via MCPConfig.ImageRef()

* feat(scripts): add China mainland mirror option to install script

Prompt users to opt-in to memoh.cn mirror during installation,
which applies docker-compose.cn.yml overlay and sets registry
in config.toml for MCP image pulls.

.air.toml

@@ -0,0 +1,22 @@
+root = "."
+tmp_dir = "tmp"
+
+[build]
+cmd = "go build -o ./tmp/memoh-server ./cmd/agent/main.go"
+bin = "./tmp/memoh-server"
+args_bin = ["serve"]
+include_ext = ["go", "toml"]
+include_dir = ["cmd", "internal", "conf"]
+exclude_dir = ["tmp", "vendor", "node_modules", "packages", "agent", "docs", "devenv", "docker", "scripts", "db/migrations"]
+exclude_regex = ["_test\\.go$"]
+delay = 1000
+stop_on_error = true
+send_interrupt = true
+kill_delay = 500
+
+[log]
+time = false
+main_only = true
+
+[misc]
+clean_on_exit = true