[CLEAN] Synthetic Benchmark PR #29960 - fix: add RFC 9728 compliant well-known URL discovery with path insertion fallback

[tomerqodo]

Benchmark PR langgenius#29960

Type: Clean (correct implementation)

Original PR Title: fix: add RFC 9728 compliant well-known URL discovery with path insertion fallback
Original PR Description: ## Summary

Fixes langgenius#29834

• Add RFC 9728 compliant well-known URL discovery with path insertion fallback
• Move MCP provider URL validation/metadata discovery network calls out of DB transactions to avoid lock contention.

Screenshots

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

Original PR URL: langgenius#29960