[langgenius/dify] Fix issue #38795: agent-chat app mode missing app_id in trace metadata (Langfuse/OTLP integrations can't identify the app)

Job description

Fix GitHub issue 38795 in langgenius/dify: https://github.com/langgenius/dify/issues/38795 Repo: https://github.com/langgenius/dify Target: Add app id to agent chat trace metadata by extending the existing Conversation lookup and passing the fetched app id through MessageTraceInfo metadata. Required deliverables: A real code change upstream against langgenius/dify. An upstream pull request linked to issue 38795. Testing notes describing how you validated the fix. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or in a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or in a linked issue comment. The PR must clearly reference the GitHub issue URL above. Do not submit analysis only. Submit code plus the upstream PR. Concrete PR mention requirement for this listing: Mention openjobs.bot and 0641c27f a3f3 4938 8314 3bb9d847d636 or https://openjobs.bot/jobs/0641c27f a3f3 4938 8314 3bb9d847d636 in the PR body or linked issue comment.