Fix Go linting errors in CI pipeline

[Copilot]

Resolves all golangci-lint errors blocking CI. The linter enforces strict error handling, modern Go syntax, and code quality standards across ~45 enabled linters.

Key Changes

Error Handling

• Added error checking for previously unchecked file operations, JSON encoding, and git operations
• Fixed shadow variable declarations by renaming conflicting error variables (e.g., validateErr, headErr, matchErr)
• Refactored commitMatchesFilter() to return bool instead of (bool, error) since error was always nil

Modern Go Syntax

• Updated octal literals to Go 1.13+ format: 0644 → 0o644
• Used http.NoBody instead of nil for GET requests without body
• Combined redundant parameter types: func(a string, b string) → func(a, b string)

Performance & Code Quality

• Pass 104-byte TaskSystemConfig by pointer to reduce allocations
• Extract repeated string literal "git" into DefaultVCSType constant
• Replace len(str) == 0 with str == "" for clarity

Security

• Tighten generated file permissions from 0644 to 0600 in report generator

Example

// Before: shadow variable error
settings, err := loadSettings()
if err != nil {
    return err
}
if err := settings.Validate(); err != nil {  // shadows outer err
    return err
}

// After: distinct variable name
settings, err := loadSettings()
if err != nil {
    return err
}
if validateErr := settings.Validate(); validateErr != nil {
    return fmt.Errorf("invalid settings: %w", validateErr)
}

Two revive warnings remain about stuttering names (task.TaskMatch, task.TaskSystem) but are intentionally not renamed to preserve API compatibility.

Original prompt

Fix the Go linting errors identified in the 'Lint' step of the CI pipeline. Ensure all Go code adheres to the linting rules using golangci-lint. This involves modifying the code to comply with project-defined linting standards and best practices. Ensure that after your changes, the linting step passes on all operating systems in the matrix. Specifically, check that the 'Lint' job as defined in the GitHub Actions pipeline workflow will succeed after the changes. Verify that the Go version compatibility and the existing matrix structure don’t get affected by the fixes.

This pull request was created from Copilot chat.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.