feat(model): add card layout block

[zimeg]

Summary

Adds support for the Block Kit card layout block to slack-api-model.

A card displays a compact, structured summary of content. It can be used on its own or grouped together inside a carousel. At least one of hero_image, title, actions, or body must be provided.

Changes

• CardBlock — new LayoutBlock model with fields heroImage (image element), icon (image element), slackIcon, title, subtitle, body, subtext (text objects), actions (list of interactive elements, e.g. buttons), and blockId, following the existing block model conventions (Lombok @Data @Builder @NoArgsConstructor @AllArgsConstructor, TYPE constant).
• GsonLayoutBlockFactory — registers the card type for deserialization.
• Blocks — adds a card(...) DSL helper mirroring the other block factories.
• BlockKitTest — adds parseCardBlock (deserialize the docs example + JSON round-trip) and buildCardBlock (builder/DSL + serialize round-trip).

Reference

Block schema: https://docs.slack.dev/reference/block-kit/blocks/card-block

Validation

Ran the touched module's build + tests:

./mvnw -pl slack-api-model -am test -Dtest=BlockKitTest

Result: BUILD SUCCESS — Tests run: 45, Failures: 0, Errors: 0, Skipped: 0 (includes the two new card tests).

Note: JaCoCo coverage instrumentation (jacoco-maven-plugin 0.8.7) is incompatible with the only JDK available in this environment (Java 25 — Unsupported class file major version 69), so the test run was executed with -Djacoco.skip=true. This is an unrelated toolchain limitation; compilation and the tests themselves pass cleanly.

🤖 Generated with Claude Code

Co-Authored-By: Claude svc-devxp-claude@slack-corp.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.29%. Comparing base (a312395) to head (0712684).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1609      +/-   ##
============================================
- Coverage     73.32%   73.29%   -0.04%     
- Complexity     4520     4521       +1     
============================================
  Files           478      478              
  Lines         14300    14302       +2     
  Branches       1490     1490              
============================================
- Hits          10486    10482       -4     
- Misses         2923     2932       +9     
+ Partials        891      888       -3     

Flag	Coverage Δ
jdk-14	73.29% <100.00%> (-0.04%)	⬇️

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