chore(catalog): record boot-3.4.12+rebuild.1

[github-actions]

Adds boot 3.4.12 → boot-3.4.12+rebuild.1 and the converted tree under markdown/boot/3.4.12/, published by the release workflow.

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Summary by cubic

Updates the Spring Boot 3.4.12 catalog entry to point at the rebuilt release boot-3.4.12+rebuild.1 and regenerates the Markdown docs so version placeholders like {version-spring-boot} and {version-graal} are replaced with explicit values.

• The catalog entry now uses the new tag and release timestamp.
• All affected docs under markdown/boot/3.4.12/ now show the concrete version strings in examples and output.

^{Written for commit 2632a14. Summary will update on new commits.}

[greptile-apps]

PR author is in the excluded authors list.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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TIP This summary will be updated as you push new changes.}

[amondnet]

Superseded by #247, which records all 47 Boot rebuilds in one commit.