#2276: Add Backlog section documenting how to find a new story

[krystynaShatkovska]

This PR fixes #2276

Implemented changes:

• Added a new "Backlog" section to documentation/contributing/issue.adoc with a step-by-step guide on how to find and pick a new story from the project backlog — including the
  issue query link, explanation of ready-to-implement and good-first-issue labels, consideration of Priority/Size for experienced contributors, and a reminder to self-assign
  before starting work

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Testing instructions

1. Open documentation/contributing/issue.adoc and verify that the new == Backlog section appears before == Working on an Issue
2. Check that the linked issue query URL opens the correct filtered issue list:
   https://github.com/devonfw/IDEasy/issues?q=is%3Aissue%20state%3Aopen%20no%3Aassignee%20label%3Aready-to-implement
3. Verify that the cross-reference link to project-board.adoc resolves correctly
4. Confirm that no content from the existing "Working on an Issue" section was lost or broken

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Checklist for this PR

Make sure everything is checked before merging this PR. For further info please also see
our DoD.

• When running mvn clean test locally all tests pass and build is successful
• PR title is of the form #«issue-id»: «brief summary» (e.g. Bump jackson.version from 2.18.0 to 2.18.2 #921: fixed setup.bat). If no issue ID exists, title only.
• PR top-level comment summarizes what has been done and contains link to addressed issue(s)
• PR and issue(s) have suitable labels
• Issue is set to In Progress and assigned to you or there is no issue (might happen for very small PRs)
• You followed all coding conventions
• You have added the issue implemented by your PR in CHANGELOG.adoc unless issue is labeled
  with internal
• You have formulated clear instructions on how to test your contribution under "Testing instructions"

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Notes:

• I removed the "Checklist for tool commandlets" section since this PR doesn't add a commandlet (as instructed)
• Don't check the boxes yet — the instructions say to check them after the PR is created
• The PR title should be: Create documentation how to find story from Backlog #2276: Add Backlog section documenting how to find a new story

[coveralls]

Coverage Report for CI Build 31683252955

Coverage remained the same at 72.887%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	17548
Covered Lines:	13340
Line Coverage:	76.02%
Relevant Branches:	7757
Covered Branches:	5104
Branch Coverage:	65.8%
Branches in Coverage %:	Yes
Coverage Strength:	3.23 hits per line

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💛 - Coveralls

[Hiepiscus]

@krystynaShatkovska Looks good to me. The new section clearly explains how to find a suitable issue from the backlog and covers all points from the issue description. One thing I noticed, I think there is a typo in the rendered URL, so the project board link does not resolve correctly.

[hohwille]

@krystynaShatkovska thank you for your PR. This is a great improvement. 👍
I only have marginal nice-to-have suggestions for you.