fix(bitbucket-cloud): resolve CEL expression failure on push events

[zakisk]

Bitbucket Cloud push events set processedEvent.Event to the string "push", but CEL evaluation expects Event to be a JSON object (map[string]interface{}). This caused all CEL expressions to fail with "cannot unmarshal string into Go value of type map[string]interface{}". Remove the incorrect Event assignment and use triggertype constants for TriggerTarget and EventType.

Assisted-by: Claude Opus 4.6 (via Claude Code)

📝 Description of the Change

🔗 Linked GitHub Issue

Fixes #2335

🧪 Testing Strategy

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[gemini-code-assist]

Code Review

This pull request refactors Bitbucket Cloud payload parsing to use typed trigger constants and introduces a new E2E test for CEL expressions on push events. It also refactors test helpers to support push-only scenarios by separating branch creation from pull request creation and updating the teardown logic to handle cases without a pull request number. I have no feedback to provide.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.00%. Comparing base (6b69972) to head (f4c95c1).
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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2704      +/-   ##
==========================================
- Coverage   59.00%   59.00%   -0.01%     
==========================================
  Files         208      208              
  Lines       20436    20435       -1     
==========================================
- Hits        12059    12058       -1     
  Misses       7603     7603              
  Partials      774      774              

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[theakshaypant]

LGTM