feat: add server mode

[jippi]

Work

• Implement webhook endpoint
• Configure project/group/global level webhook targeting /gitlab endpoint
• Supports Comments (note event)
• Supports Merge request events (merge_request event)
• Add webhook_event Expr variable value with the full raw event payload sent from the GitLab server. (NULL in non-server mode)

Why

Deploy a single instance of scm-engine, with a single privileged account/token, and configure webhook at the level you want. Any project can start to use scm-engine by simply putting an scm-engine.yml file in the location configured on the server (default: /.scm-engine.yml)

No additional overhead, security, or compliance considerations.

Workflow

1. Does a partial decode of the payload to extract details needed
   • project.path_with_namespace
   • merge_request.iid (project level id for the MR)
   • merge_request.last_commit.id (git SHA)
2. Tries to grab the $SCM_ENGINE_CONFIG_FILE (-config-file) from the repo over HTTP API
3. Parses config file
4. Processes the config file

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 507 lines in your changes are missing coverage. Please review.

Project coverage is 0.00%. Comparing base (ca1bb19) to head (532eb2c).
Report is 12 commits behind head on main.

Files	Patch %	Lines
pkg/tui/printer.go	0.00%	125 Missing ⚠️
cmd/cmd_server.go	0.00%	92 Missing ⚠️
pkg/tui/logger.go	0.00%	53 Missing ⚠️
pkg/tui/style.go	0.00%	52 Missing ⚠️
pkg/tui/theme.go	0.00%	33 Missing ⚠️
pkg/tui/context.go	0.00%	32 Missing ⚠️
main.go	0.00%	25 Missing ⚠️
pkg/tui/writer.go	0.00%	23 Missing ⚠️
pkg/tui/helpers.go	0.00%	20 Missing ⚠️
cmd/shared.go	0.00%	14 Missing ⚠️
... and 7 more

Additional details and impacted files

@@          Coverage Diff           @@
##            main     #12    +/-   ##
======================================
  Coverage   0.00%   0.00%            
======================================
  Files         20      30    +10     
  Lines        730    1405   +675     
======================================
- Misses       730    1405   +675     

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