Add 'validate-rebase-rules' skill

[RomanNikitenko]

What does this PR do?

• Adds validate-rebase-rules skill
• Allows to automate validation process of rebase rules (replace, add, override)
• Generates a rebase-rules-validation.md report with mismatches and proposed fixes.
• it's used when asked to check, validate, or audit rebase rules, or before a rebase.

What issues does this PR fix?

eclipse-che/che#23749

I used the skill to validate rebase rules for the current alignment with upstream: #646

How to test this PR?

• run Claude
• type validate-rebase-rules
• a report should be generated with detected problems
• Example of the report with detected problems is: https://github.com/RomanNikitenko/che-code/blob/add-validate-rebase-rules-skill/rebase-rules-validation.md
• The report is not going to be merged, it's going to be used to fix found issues.

Does this PR contain changes that override default upstream Code-OSS behavior?

• the PR contains changes in the code folder (you can skip it if your changes are placed in a che extension )
• the corresponding items were added to the CHANGELOG.md file
• rules for automatic git rebase were added to the .rebase folder

Generated-by: Cursor AI

[github-actions]

Click here to review and test in web IDE:

[RomanNikitenko]

this file is not going to be merged
it's just as an example of detected problems

[RomanNikitenko]

this file should be merged to the main within another PR: #676

[RomanNikitenko]

variables are used by skills
Also this place

che-code/rebase.sh

Line 592 in 73bb214

UPSTREAM_VERSION=$(git rev-parse upstream-code/release/1.104)

should use CURRENT_UPSTREAM_VERSION variable

[RomanNikitenko]

The PR depends on

• #676
• #646

[github-actions]

Pull Request images published ✨

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Dev image: quay.io/che-incubator-pull-requests/che-code-dev:pr-681-dev-amd64

[github-actions]

Pull Request images published ✨

Editor amd64: quay.io/che-incubator-pull-requests/che-code:pr-681-amd64
Editor arm64: quay.io/che-incubator-pull-requests/che-code:pr-681-arm64
Dev image: quay.io/che-incubator-pull-requests/che-code-dev:pr-681-dev-amd64

[github-actions]

Pull Request images published ✨

Editor amd64: quay.io/che-incubator-pull-requests/che-code:pr-681-amd64
Editor arm64: quay.io/che-incubator-pull-requests/che-code:pr-681-arm64
Dev image: quay.io/che-incubator-pull-requests/che-code-dev:pr-681-dev-amd64