feat(build-trigger): trigger build on Buck file upload completion

[VansamaYD]

• Add BuckFileUploadHandler and register it in TriggerRegistry
• Add TriggerContext::from_buck_upload and BuckFileUploadPayload
• Add trigger_build_for_buck_upload in MonoApiService::complete_buck_upload
• Extend CompleteResponse with repo_path and from_hash for trigger context

link #1831

[Copilot]

Pull request overview

This PR integrates Buck file uploads into Mega's explicit build trigger system, addressing issue #1831. Previously, Buck file uploads (via cargo buckal) were not systematically integrated into the unified build trigger model. This PR adds a new BuckFileUploadHandler that triggers builds when Buck files are uploaded, providing the same observability and control as Git push and manual triggers.

Changes:

• Added BuckFileUploadHandler to handle Buck file upload build triggers
• Extended CompleteResponse model with repo_path and from_hash fields for build trigger context
• Integrated build triggering into complete_buck_upload API endpoint using async spawn pattern

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
ceres/src/build_trigger/buck_upload_handler.rs	New handler implementing TriggerHandler for Buck file uploads, follows established handler pattern with ChangesCalculator
ceres/src/build_trigger/mod.rs	Registers BuckFileUploadHandler in TriggerRegistry alongside other trigger handlers
ceres/src/build_trigger/model.rs	Updates ListTriggersParams comment to include buck_file_upload in the list of trigger types
ceres/src/api_service/mono_api_service.rs	Adds trigger_build_for_buck_upload method and integrates it into complete_buck_upload endpoint
ceres/src/model/buck.rs	Extends CompleteResponse with repo_path and from_hash fields needed for trigger context