Add agentex_dev_doctor for OSS local dev preflight

[Abhishek21g]

Problem

External contributors hit failed local onboarding when Docker, ports, or DOCKER_REGISTRY point at private ECR (#163). Main Dockerfile now uses public bases, but env/port conflicts remain a common footgun.

Fix

• scripts/agentex_dev_doctor.py — checks docker, uv, compose file, ports 6379/5432/5003, and private ECR DOCKER_REGISTRY
• docs/LOCAL_DEV.md — OSS contributor troubleshooting
• README pointer before Setup
• Unit tests in agentex/tests/unit/scripts/test_dev_doctor.py

Verification

python scripts/agentex_dev_doctor.py
python -m unittest agentex.tests.unit.scripts.test_dev_doctor -v

Relates to #163

Greptile Summary

This PR adds scripts/agentex_dev_doctor.py, a standalone preflight script that checks docker, uv, the compose file, critical ports (6379/5432/5003), and DOCKER_REGISTRY for private ECR misconfiguration — targeting the OSS onboarding failures described in #163. A new docs/LOCAL_DEV.md and a README pointer accompany the script, along with three unit tests.

• agentex_dev_doctor.py is well-structured: _port_free no longer sets SO_REUSEADDR, the warn-gate filtering in run_doctor() correctly excludes non-ECR custom registries from failing the overall check, and all subprocess calls use timeout and capture_output.
• agentex/tests/unit/scripts/__init__.py is absent; the python -m unittest verification command in the PR description will raise ModuleNotFoundError before any test runs.
• _check_docker_daemon() always fires even when the docker binary is absent, producing two consecutive FAIL entries for the same underlying cause.

Confidence Score: 4/5

Safe to merge for the script and docs; the test file needs a one-line init.py added alongside it to make the documented verification command work.

The doctor script and documentation are correct and self-contained. The test file itself works under pytest, but the python -m unittest command in the PR description fails immediately because agentex/tests/unit/scripts/init.py does not exist — every other test subdirectory at that depth has one.

agentex/tests/unit/scripts/ — needs an init.py so the documented python -m unittest verification command resolves the package correctly.

Important Files Changed

Filename	Overview
scripts/agentex_dev_doctor.py	New preflight script: checks docker binary, daemon, uv, compose file, ports (6379/5432/5003), and DOCKER_REGISTRY for private ECR; logic is sound, warn-gate filtering and exit code are correct.
agentex/tests/unit/scripts/test_dev_doctor.py	Uses importlib.util.spec_from_file_location matching the existing sibling pattern, but agentex/tests/unit/scripts/init.py is missing so the python -m unittest verification command in the PR description fails with ModuleNotFoundError.
docs/LOCAL_DEV.md	New troubleshooting doc with accurate symptom/fix table; links correctly to the issue and doctor script.
README.md	Adds a one-line pointer to the dev doctor script and LOCAL_DEV.md before the Setup section; no content issues.

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