Unify User-Agent to CKAN-MCP-Server/1.0 across all tools

[aborruso]

Problem

The server currently uses inconsistent User-Agent strings depending on the operation:

• CKAN-MCP-Server/1.0 — CKAN API calls, quality checks, portal discovery
• Mozilla/5.0 (compatible; CKAN-MCP-Server/1.0) — SPARQL queries
• Mozilla/5.0 (X11; Linux x86_64) ... Chrome/120 — direct file downloads (src/utils/http.ts)

The Chrome UA was added to avoid portals that block non-browser requests, but it's not transparent.

Proposed Change

Unify all tools to use CKAN-MCP-Server/1.0.

Before Implementing

• Test locally that all affected tools still work after the change
• Verify file downloads (CSV) still succeed with the honest UA
• Run full test suite: npm test
• Run end-to-end HTTP server tests against real portals

Files to Change

• src/utils/http.ts — two occurrences (Node.js axios path + Workers fetch path)
• src/tools/sparql.ts — one occurrence