docs(skills): publish 10 SKILL.md manifests for external AI agents

Adds /skills/omniroute*/SKILL.md following the Anthropic skill manifest
spec (frontmatter name/description + self-contained body): chat, image,
tts, stt, embeddings, web-search, web-fetch, mcp, a2a + entry point.

External agents (Claude Desktop, ChatGPT, Cursor, Cline) can fetch one
raw GitHub URL to learn how to call OmniRoute — zero-friction onboarding.
OmniRoute-specific differentiators (mcp + a2a skills) extend the 9router
pattern with 2 extra manifests not present in the reference.

Adds structural lint test (tests/unit/docs/skillManifestsLint.test.ts)
enforcing frontmatter, env-var references, and trigger-phrase quality.

Adds "AI Agent Skills" section to README.md root.

Ref: 9router/skills/ pattern (adapted).

README.md

@@ -460,6 +460,19 @@ Alibaba · Amazon Q · AssemblyAI · Baidu Qianfan · Baseten · Black Forest La
 
 ---
 
+## 🤖 AI Agent Skills
+
+Drop-in markdown manifests that let any AI agent consume OmniRoute via one fetch.
+
+Tell your agent (Claude Desktop, ChatGPT, Cursor, Cline, etc.):
+
+> "Fetch this URL and use OmniRoute according to its instructions:
+> `https://raw.githubusercontent.com/NomenAK/OmniRoute/main/skills/omniroute/SKILL.md`"
+
+10 skills available — see [skills/README.md](./skills/README.md).
+
+---
+
 ## 🔄 How It Works
 
 ```