refactor(exgentic_a2a_runner): vendor benchmark and agent env templates

[kellyaa]

Summary

• deploy-benchmark.sh and deploy-agent.sh were fetching .env templates at deploy time from yoavkatz/agent-examples on the transient feature/exgentic-mcp-server branch. If that branch is renamed, force-pushed, or the fork disappears, every deploy breaks — and any upstream edit silently changes deployed workloads with no diff in this repo.
• Vendors the five upstream files into exgentic_a2a_runner/env/ (mirroring the upstream path layout) and replaces the curl fetch with a local file read. The parse-env API call is preserved unchanged; only the source of the raw text moves from HTTP to filesystem.
• Files copied byte-identical from upstream at vendoring time: .env.gsm8k, .env.tau2, .env.appworld (benchmarks) and .env.example, .env.advanced (agents). .env.advanced and .env.appworld are not referenced by current scripts but are vendored for parity.
• docs/workflow-diagrams.md sequence and component diagrams updated to show a vendored env/ filesystem node instead of a GitHub-raw node.
• .gitignore — removed redundant env/ and ENV/ virtualenv-convention ignores that were blocking the vendored directory. venv/ and .venv still cover Python virtualenvs.

Test plan

• bash -n on both scripts — parse cleanly.
• grep -rn "raw.githubusercontent.com/yoavkatz|feature/exgentic-mcp-server" exgentic_a2a_runner/ — no matches.
• grep -nE "GH as GitHub|GitHub raw" exgentic_a2a_runner/docs/workflow-diagrams.md — no matches.
• diff each vendored file against upstream at vendoring time — all identical.
• git check-ignore on the vendored files — none ignored after .gitignore cleanup.
• End-to-end kind deploy of a benchmark (e.g. ./deploy-and-evaluate.sh --benchmark gsm8k --agent tool_calling) to confirm the parse-env pipeline still receives the expected content and the deployed pod comes up ready.
• Reviewer sanity: confirm no tests / CI / Makefile targets exercise these deploy scripts (search returned nothing at plan time).

Notes

• No remote-override escape hatch was added. If someone needs different env values, they edit env/**/*.env* in-tree and commit — which is the whole point of vendoring.
• authbridge/intent_prompt.txt still allows raw.githubusercontent.com for the deployed agents own runtime traffic (e.g. litellms model-pricing JSON). That is unrelated to the deploy-time fetch removed here.