feat(skills): add 6 due-diligence data-source skills (#111)

## Summary

Adds six enterprise due-diligence data-source skills as local built-in
skills (SKILL.md + SKILL.zh-CN.md + catalog-metadata sidecar), per
ADR-038.

| Skill | Category | Risk | Source |
|---|---|---|---|
| baidu-poi-search | data | low | Baidu Map Place API (REST) |
| tianyancha-risk | business | low | Tianyancha risk API (REST) |
| ccgp-gov-procurement | business | medium | ccgp.gov.cn (WebBridge) |
| cnipa-patent-search | business | medium | CNIPA pss-system (WebBridge)
|
| creditchina-query | business | high | creditchina.gov.cn (WebBridge +
ddddocr) |
| multi-source-sentiment | research | medium | Douyin Index/Featured +
WebSearch |

## Changes
- 6 x skills/<id>/{SKILL.md, SKILL.zh-CN.md, catalog-metadata.v1.json}
- builtin-skills.json: 34 -> 40
- manifest.json: totalSkills 63 -> 69
- README.md counts + list

## Security
- Credentials replaced with env-var placeholders (BAIDU_MAP_AK,
TIANYANCHA_TOKEN); verified no secrets in diff

## Validation
- validate-i18n.py: 0 errors (remaining warnings pre-existing repo-wide)
- zh/en heading parity verified; source_hash computed per repo algorithm

Co-authored-by: yi-ge <yi-ge@desirecore.net>

builtin-skills.json

@@ -1,9 +1,13 @@
 {
   "skills": [
+    "baidu-poi-search",
+    "ccgp-gov-procurement",
     "clone-agent",
+    "cnipa-patent-search",
     "code-intelligence",
     "configuring-compute",
     "create-agent",
+    "creditchina-query",
     "dashscope-image-gen",
     "delete-agent",
     "dev-environment-setup",
@@ -18,6 +22,7 @@
     "markdown",
     "minimax-music-gen",
     "minimax-video-gen",
+    "multi-source-sentiment",
     "nodejs-runtime",
     "pdf",
     "pptx",
@@ -27,6 +32,7 @@
     "s3-storage-operations",
     "skill-creator",
     "tech-diagram",
+    "tianyancha-risk",
     "update-agent",
     "using-services",
     "web-access",