docs: refresh deployment/testing guides and remove stale investigation report

[CJackHwang]

Motivation

• Clean up outdated/unreferenced documentation and avoid misleading deployment instructions that implied DS2API_CONFIG_JSON was required for local docker-compose use.
• Keep the repo tidy by removing a stale investigation note that is no longer referenced by code or docs.

Description

• Simplified Docker setup steps in README.MD and README.en.md to require at least DS2API_ADMIN_KEY in .env and removed the suggestion to always generate DS2API_CONFIG_JSON for local docker-compose runs.
• Made the same minimalization change in DEPLOY.md and DEPLOY.en.md so English/Chinese docs stay consistent with runtime behavior.
• Synchronized TESTING.md preflight instructions to match the actual hardcoded Node preflight command list (node --test tests/node/stream-tool-sieve.test.js tests/node/chat-stream.test.js tests/node/js_compat_test.js).
• Removed the unreferenced historical report file misc/deepseek_functioncalling_bug/report.md to reduce repository noise.

Testing

• Ran go test ./... and it completed successfully with all Go unit packages passing.
• No runtime code paths were modified, so no additional build or integration tests were required.

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Codex Task

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Project	Deployment	Actions	Updated (UTC)
ds2api	Ready	Preview, Comment	Mar 19, 2026 7:06pm