feat: support custom package index (UV_DEFAULT_INDEX) for Container builds

[jesseturner21]

Description

Enterprise customers that enforce internal artifact repositories (instead of public PyPI) cannot build Container agents because uv sync in the Dockerfile defaults to PyPI. This PR adds support for configuring custom uv package index URLs via ~/.agentcore/config.json, which the CLI forwards as Docker --build-arg flags during all container image builds.

Uses the current (non-deprecated) uv environment variables UV_DEFAULT_INDEX and UV_INDEX per uv docs.

Configuration: Users add their index URLs once to ~/.agentcore/config.json:

{
  "uvDefaultIndex": "https://my-enterprise-repo/simple",
  "uvIndex": "https://another-repo/simple"
}

How it works:

• New readCliConfig() utility reads ~/.agentcore/config.json (silently returns empty object if missing/malformed)
• New getUvBuildArgs() helper converts config into --build-arg UV_DEFAULT_INDEX=... flags
• Dockerfile template declares ARG UV_DEFAULT_INDEX / ARG UV_INDEX and sets them as ENV so all uv commands respect them
• Build args are forwarded in all three Docker build call sites: dev base image, dev layer, and package/deploy

When no config is present, build args are empty and uv falls back to PyPI — fully backward-compatible.

Related Issue

Closes #

Documentation PR

N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Manual testing:

• Without config: agentcore dev builds and runs Container agent successfully using default PyPI
• With config (uvDefaultIndex: "https://pypi.org/simple"): Full end-to-end build succeeds; docker inspect confirms UV_DEFAULT_INDEX=https://pypi.org/simple is set in the built image
• With fake enterprise URL: Build correctly fails with DNS error for the custom index, confirming args are forwarded into the Docker build context
• Malformed/missing config: Gracefully returns empty args, no errors

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the
terms of your choice.

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	44.15%	3000 / 6795
🔵	Statements	43.72%	3159 / 7224
🔵	Functions	45.96%	621 / 1351
🔵	Branches	48.74%	1960 / 4021

Generated in workflow #726 for commit 353afc1 by the Vitest Coverage Report Action