feat(config): Add retry configuration

[tab]

• Add retry fields to Config with defaults
• Add validation for retry attempts and backoff
• Modify Load and DefaultConfig to handle retry settings

[Copilot]

Pull request overview

This PR adds retry configuration support to the application with configurable attempts and backoff duration. The changes introduce retry settings to the Config struct, add validation for these settings, and update all code to use the centralized configuration instead of hard-coded constants.

Changes:

• Added Retry struct to Config with Attempts and Backoff fields
• Renamed constant from RetryAttempt to RetryAttempts for consistency
• Updated all runner code to reference cfg.Retry instead of package-level constants

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/config/constants.go	Renamed constant from RetryAttempt to RetryAttempts
internal/config/config.go	Added Retry struct to Config and validation logic
internal/config/config_test.go	Added comprehensive tests for retry configuration and validation
internal/app/runner/runner.go	Updated to use cfg.Retry instead of package constants
internal/app/runner/runner_test.go	Updated test mocks to use DefaultConfig() for proper initialization
internal/app/errors/errors.go	Added error constants for retry validation
fuku.yaml	Added retry configuration example

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.62%. Comparing base (8597657) to head (517d5e5).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #50      +/-   ##
==========================================
+ Coverage   87.57%   87.62%   +0.04%     
==========================================
  Files          34       34              
  Lines        2591     2601      +10     
==========================================
+ Hits         2269     2279      +10     
  Misses        284      284              
  Partials       38       38              

Files with missing lines	Coverage Δ
internal/app/runner/runner.go	97.10% <100.00%> (ø)
internal/config/config.go	89.54% <100.00%> (+0.73%)	⬆️

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