feat(zephyr-agent): show outdated version warning in plugins

[Nsttt]

What's added in this PR?

Implements plugin-side outdated-version UX directly in zephyr-agent (no gateway/header dependency).

Details:

• Added local outdated check during ZephyrEngine.create:
  • resolves active plugin package name from app dependencies + builder fallback
  • fetches latest version from npm dist-tags
  • compares current vs latest and prints a one-time terminal error-style warning when outdated
• Warning copy now:
  • Your Zephyr Plugin version is outdated ...
  • If you are facing any issue, upgrade <plugin-package-name> first.
• Removed previous header-based warning path from HTTP/resolve request flows.
• Added runtime-safe handling for unknown builder strings (fixes BUILDER_PLUGIN_CANDIDATES[builder] is not iterable).

Screenshots

N/A (terminal output only)

What's the issues or discussion related to this PR ?

Context: users on older plugin versions should get immediate troubleshooting guidance from the plugin itself, without requiring API gateway support.

What are the steps to test this PR?

1. Run:
   • pnpm nx test zephyr-agent --runInBand
   • pnpm nx build zephyr-agent
2. For outdated warning behavior, mock npm dist-tags response to a higher latest than current and verify one warning is printed.
3. For resolver robustness, verify unknown builder inputs do not throw and fallback package name is used.

Documentation update for this PR (if applicable)?

No docs update in this PR.

(Optional) What's left to be done for this PR?

None.

(Optional) What's the potential risk and how to mitigate it?

Risk: extra npm registry request on initialization.
Mitigation: non-blocking behavior; failures to fetch latest are ignored.

(Required) Pre-PR/Merge checklist

• I have added/updated/opened a PR to documentation to cover this new behavior
• I have added an explanation of my changes
• I have written new tests (if applicable)
• I have tested this locally (standing from a first time user point of view, never touch this app before)
• I have/will run tests, or ask for help to add test

[Copilot]

Pull request overview

Adds a plugin-facing terminal warning intended to notify users when their Zephyr plugin version is outdated, plus utilities/tests to determine which Zephyr plugin package is in use.

Changes:

• Added resolveZephyrPluginPackageName() to infer the Zephyr plugin package name from an app’s package.json deps.
• Added maybeShowOutdatedPluginWarning() which checks npm dist-tags and emits a one-time console error warning.
• Hooked the warning into ZephyrEngine.create() and added Jest coverage for the new utilities.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
libs/zephyr-agent/src/zephyr-engine/index.ts	Calls the new outdated-warning logic during engine initialization.
libs/zephyr-agent/src/lib/version/plugin-package-name.ts	Implements plugin package name resolution based on builder + declared deps.
libs/zephyr-agent/src/lib/version/plugin-package-name.test.ts	Tests plugin package name resolution + fallback behavior.
libs/zephyr-agent/src/lib/version/outdated-plugin-warning.ts	Implements npm-registry-based latest-version lookup + warning emission.
libs/zephyr-agent/src/lib/version/outdated-plugin-warning.test.ts	Tests warning emission, non-emission, and one-time behavior.

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