fix: replace hardcoded ~/.desirecore paths with ${DESIRECORE_ROOT} variable (#16)

## Summary

- 将所有技能文件中的硬编码 `~/.desirecore/` 和 `$HOME/.desirecore/` 路径替换为
`${DESIRECORE_ROOT}/` 变量
- 递增 manifest.json version 至 1.2.1

## Why

dev 模式下 `DESIRECORE_HOME=~/.desirecore-dev`，硬编码路径导致技能读取错误的端口文件和目录。主仓库的
`variable-substitutor.ts` 会在运行时将 `${DESIRECORE_ROOT}` 替换为实际根目录。

## Test plan

- [ ] `npm run dev` 启动后触发任意技能，确认端口路径解析为
`~/.desirecore-dev/agent-service.port`
- [ ] prod 模式确认路径为 `~/.desirecore/agent-service.port`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

skills/manage-skills/SKILL.md

@@ -222,10 +222,10 @@ POST /api/agents/{agentId}/skills
 
 ```bash
 # Sidecar file path for a global Skill
-~/.desirecore/skills/{skillId}/{filename}
+${DESIRECORE_ROOT}/skills/{skillId}/{filename}
 
 # Sidecar file path for an Agent-scoped Skill
-~/.desirecore/agents/{agentId}/skills/{skillId}/{filename}
+${DESIRECORE_ROOT}/agents/{agentId}/skills/{skillId}/{filename}
 ```
 
 ### 3. Manage Existing Skills via API
@@ -351,7 +351,7 @@ When you need to create a Skill from scratch or the API approach is not flexible
 **Global Skill** (visible to all Agents):
 
 ```
-~/.desirecore/skills/
+${DESIRECORE_ROOT}/skills/
 └── my-new-skill/
     ├── SKILL.md          # required: skill definition file
     ├── examples/          # optional: example files
@@ -362,7 +362,7 @@ When you need to create a Skill from scratch or the API approach is not flexible
 **Agent-scoped Skill** (visible only to the specified Agent):
 
 ```
-~/.desirecore/agents/{agentId}/
+${DESIRECORE_ROOT}/agents/{agentId}/
 └── skills/
     └── my-new-skill/
         ├── SKILL.md
@@ -441,7 +441,7 @@ Describe the execution flow, API calls, and input/output formats stage by stage
 The following example shows how to create a global Skill with the Write tool:
 
 ```
-Target path: ~/.desirecore/skills/daily-summary/SKILL.md
+Target path: ${DESIRECORE_ROOT}/skills/daily-summary/SKILL.md
 ```
 
 Content to write:
@@ -535,8 +535,8 @@ Skills exist at three scope levels, listed from highest priority to lowest:
 | Priority | Scope     | Path                                     | Visibility           |
 | ------ | ---------- | ---------------------------------------- | ------------------ |
 | Highest   | Project | `.claude/skills/` (project root)           | All Agents in the current project |
-| Medium     | Agent   | `~/.desirecore/agents/{agentId}/skills/` | Only that Agent         |
-| Lowest    | Global  | `~/.desirecore/skills/`                  | All Agents         |
+| Medium     | Agent   | `${DESIRECORE_ROOT}/agents/{agentId}/skills/` | Only that Agent         |
+| Lowest    | Global  | `${DESIRECORE_ROOT}/skills/`                  | All Agents         |
 
 **Same-name override rule**: a Skill in a higher-priority scope overrides a same-named Skill in a lower-priority scope. For example, an Agent-scoped `data-analysis` Skill will shadow a global Skill of the same name.