Replace local schema with remote source of truth

[Copilot]

The MCP Gateway was maintaining a local copy of the JSON schema instead of referencing the canonical version at https://raw.githubusercontent.com/githubnext/gh-aw/main/docs/public/schemas/mcp-gateway-config.schema.json.

Changes

• Removed local schema file (internal/config/schemas/mcp-gateway-config.schema.json)
• Fetch schema at runtime from remote URL instead of embedding with go:embed
• Fix regex incompatibility: Remote schema uses negative lookahead patterns (^(?!stdio$|http$)[a-z][a-z0-9-]*$) which aren't valid in JSON Schema Draft 7. Transform to equivalent not constraints:

  // Before: Pattern with negative lookahead (invalid)
  typeField["pattern"] = "^(?!stdio$|http$)[a-z][a-z0-9-]*$"
  
  // After: Use 'not' constraint (valid)
  typeField["not"] = map[string]interface{}{
      "enum": []string{"stdio", "http"},
  }

• Update mount validation: Remote schema allows optional mode (source:dest or source:dest:mode). Updated regex pattern and validation logic accordingly
• Update schema URL references in rules.go to point to raw GitHub content URL

Schema Compatibility

The remote schema includes features not yet implemented (custom server types, tools filter). Validation accepts these but runtime ignores them, maintaining backward compatibility.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>mcp schema authority</issue_title>
<issue_description>this should be the Source of Truth. https://github.com/githubnext/gh-aw/blob/main/docs/public/schemas/mcp-gateway-config.schema.json

https://github.com/githubnext/gh-aw-mcpg/blob/main/internal/config/schemas/mcp-gateway-config.schema.json should refer to that one</issue_description>

<agent_instructions>Please find references to the local schema and replace them with references to the schema in the gh-aw repo. THen remove the schema file from this repo.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes mcp schema authority #106

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.