feat: add jcode integration (was #2248, rebased and conflicts resolved)

[przeqpiciel]

Rebased follow-up to #2248 "feat: add jcode integration". The original head branch lives on 1jehuang/herdr, which the author and I have no write access to, so the resolved changes are re-submitted from przeqpiciel/herdr.

This squashes the jcode integration into a single commit on current master (d76657f2) with the upstream Qwen/OpenCode integration changes merged in:

• Preserved both the Jcode and upstream Qwen/OpenCode integration changes across CLI parsing, detection, integration registries/actions/targets, config docs, and integration docs.
• Updated the merged fixed-size target/agent registries for the combined entries (IntegrationTarget::ALL 18, Agent::ALL 23, SCREEN_MANIFEST_AGENTS 21, integration_specs 18).

Validation:

• cargo fmt --check and cargo clippy --all-targets --locked -- -D warnings pass.
• Focused merged Jcode/Qwen/OpenCode integration path: 152 tests pass.
• Public CLI acceptance: herdr integration status/install/uninstall jcode exercised against an isolated real Jcode config (PASS).
• Full-suite acceptance remains blocked only by pre-existing flaky live-handoff tests (unrelated).

Closes the delivery path blocked in #2248.

[coderabbitai]

Important

Review skipped

Auto reviews are limited based on label configuration.

🏷️ Required labels (at least one) (1)

• ai-review

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 23620f23-2ebf-4d01-9cbe-0fa97faa9572

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[kangal-bot]

Hi @przeqpiciel, thanks for your interest in contributing.

Herdr does not accept unsolicited implementation pull requests from contributors who are not listed in .github/APPROVED_CONTRIBUTORS.

The pull request author is not an approved contributor.

If you encountered a reproducible bug, report the observed behavior through the bug issue template. A report does not reserve the work or authorize a pull request; accepted fixes are normally implemented by Herdr’s maintainer-controlled agents.

Feature requests, behavior changes, and other proposals belong in GitHub Discussions. Do not open an issue merely to justify an implementation that was already written.

If a maintainer explicitly wants this implementation, they can reopen the pull request. Reopening by anyone else will be closed again automatically.

See https://github.com/herdrdev/herdr/blob/master/CONTRIBUTING.md for the contribution policy.