refactor: P0-P3 fixes, C1 cleanup, architecture diagrams, go.work upgrade

- P0-1: ProviderError type + ReportStatus for precise 401/403 detection
- P0-2: Remove -config flag from deploy/homeagent.service
- P2-1: 5s debounce on context.go Save()
- P2-2→C1: Delete output_set_channel entirely
- P2-3: Extract mediaDataURL/mediaChat helpers
- P2-4: Dedup defaultSources var
- P3: Delete dead packages (embed/tokenizer/container/snapshot)
- P3: Delete dead functions (messagesToMap, RunStageAll)
- CL: Update .gitignore, docs, Makefile, gojieba removal
- Config: Delete config/config.yaml, update docs
- Arch: Remove EmitOutputTo from emitResponse
- CL-1: go.work 1.19→1.21
- Docs: Add Mermaid architecture diagrams to README
- Docs: Add kernel-rebuild requires plugin-rebuild note to PLUGIN_DEV.md

docs/ARCHITECTURE.md

@@ -202,12 +202,11 @@ RegisterStage(stage, fn)  ──→  runStage() 在对应阶段调用
 Subscribe(event, fn)      ──→  Publish() 通知所有订阅者
 ```
 
-`internal/plugin/sdk/` 定义完整 SDK：
+`internal/sdk/` 桥接外部 SDK 接口到内核，定义完整 PluginSDK：
 
 ```go
 sdk.RegisterTool(name, def, handler)
 sdk.RegisterStage(stage, handler)
-sdk.Subscribe(eventType, handler)
 sdk.Publish(event)
 sdk.InjectInput(source, channel, payload)
 sdk.InjectInterrupt(source, channel, payload)
@@ -281,7 +280,7 @@ internal/
 │   ├── agentcli/          — PTY 终端
 │   ├── healthcheck/       — 健康检查
 │   └── pluginmgr/         — 插件管理器
-├── sdk/                   — PluginSDK 定义
+├── internal/sdk/          — PluginSDK 定义
 │   ├── plugin.go          — Plugin 接口 + PluginSDK
 │   ├── memory.go          — MemoryAPI
 │   ├── knowledge.go       — KnowledgeAPI