feat(baoyu-post-to-wechat): add multi-account support

Support multiple WeChat Official Accounts via EXTEND.md accounts block.
Each account gets isolated Chrome profile, credential resolution chain
(inline → prefixed env → unprefixed env), and --account CLI arg.

skills/baoyu-post-to-wechat/SKILL.md

@@ -95,9 +95,115 @@ chrome_profile_path: /path/to/chrome/profile
 **Value priority**:
 1. CLI arguments
 2. Frontmatter
-3. EXTEND.md
+3. EXTEND.md (account-level → global-level)
 4. Skill defaults
 
+## Multi-Account Support
+
+EXTEND.md supports managing multiple WeChat Official Accounts. When `accounts:` block is present, each account can have its own credentials, Chrome profile, and default settings.
+
+**Compatibility rules**:
+
+| Condition | Mode | Behavior |
+|-----------|------|----------|
+| No `accounts` block | Single-account | Current behavior, unchanged |
+| `accounts` with 1 entry | Single-account | Auto-select, no prompt |
+| `accounts` with 2+ entries | Multi-account | Prompt to select before publishing |
+| `accounts` with `default: true` | Multi-account | Pre-select default, user can switch |
+
+**Multi-account EXTEND.md example**:
+
+```md
+default_theme: default
+default_color: blue
+
+accounts:
+  - name: 宝玉的技术分享
+    alias: baoyu
+    default: true
+    default_publish_method: api
+    default_author: 宝玉
+    need_open_comment: 1
+    only_fans_can_comment: 0
+    app_id: wx1234567890abcdef
+    app_secret: abc123secret456
+  - name: AI工具集
+    alias: ai-tools
+    default_publish_method: browser
+    default_author: AI工具集
+    need_open_comment: 1
+    only_fans_can_comment: 0
+```
+
+**Per-account keys** (can be set per-account or globally as fallback):
+`default_publish_method`, `default_author`, `need_open_comment`, `only_fans_can_comment`, `app_id`, `app_secret`, `chrome_profile_path`
+
+**Global-only keys** (always shared across accounts):
+`default_theme`, `default_color`
+
+### Account Selection (Step 0.5)
+
+Insert between Step 0 and Step 1 in the Article Posting Workflow:
+
+```
+if no accounts block:
+    → single-account mode (current behavior)
+elif accounts.length == 1:
+    → auto-select the only account
+elif --account <alias> CLI arg:
+    → select matching account
+elif one account has default: true:
+    → pre-select, show: "Using account: <name> (--account to switch)"
+else:
+    → prompt user:
+      "Multiple WeChat accounts configured:
+       1) <name1> (<alias1>)
+       2) <name2> (<alias2>)
+       Select account [1-N]:"
+```
+
+### Credential Resolution (API Method)
+
+For a selected account with alias `{alias}`:
+
+1. `app_id` / `app_secret` inline in EXTEND.md account block
+2. Env var `WECHAT_{ALIAS}_APP_ID` / `WECHAT_{ALIAS}_APP_SECRET` (alias uppercased, hyphens → underscores)
+3. `.baoyu-skills/.env` with prefixed key `WECHAT_{ALIAS}_APP_ID`
+4. `~/.baoyu-skills/.env` with prefixed key
+5. Fallback to unprefixed `WECHAT_APP_ID` / `WECHAT_APP_SECRET`
+
+**.env multi-account example**:
+
+```bash
+# Account: baoyu
+WECHAT_BAOYU_APP_ID=wx1234567890abcdef
+WECHAT_BAOYU_APP_SECRET=abc123secret456
+
+# Account: ai-tools
+WECHAT_AI_TOOLS_APP_ID=wxabcdef1234567890
+WECHAT_AI_TOOLS_APP_SECRET=def789secret012
+```
+
+### Chrome Profile (Browser Method)
+
+Each account uses an isolated Chrome profile for independent login sessions:
+
+| Source | Path |
+|--------|------|
+| Account `chrome_profile_path` in EXTEND.md | Use as-is |
+| Auto-generated from alias | `{shared_profile_parent}/wechat-{alias}/` |
+| Single-account fallback | Shared default profile (current behavior) |
+
+### CLI `--account` Argument
+
+All publishing scripts accept `--account <alias>`:
+
+```bash
+${BUN_X} {baseDir}/scripts/wechat-api.ts <file> --theme default --account ai-tools
+${BUN_X} {baseDir}/scripts/wechat-article.ts --markdown <file> --theme default --account baoyu
+${BUN_X} {baseDir}/scripts/wechat-browser.ts --markdown <file> --images ./photos/ --account baoyu
+```
+
 ## Pre-flight Check (Optional)
 
 Before first use, suggest running the environment check. User can skip if they prefer.
@@ -139,6 +245,7 @@ Copy this checklist and check off items as you complete them:
 ```
 Publishing Progress:
 - [ ] Step 0: Load preferences (EXTEND.md)
+- [ ] Step 0.5: Resolve account (multi-account only)
 - [ ] Step 1: Determine input type
 - [ ] Step 2: Select method and configure credentials
 - [ ] Step 3: Resolve theme/color and validate metadata