chore: linter added + failover placeholder

[SantiagoDePolonia]

• added a go linter
• added a failover config file mock
• fixed syntax with the linter

[Copilot]

Pull request overview

This PR introduces golangci-lint for code quality enforcement and addresses linter warnings throughout the codebase. It also adds a placeholder failover configuration file.

• Adds golangci-lint configuration with essential linters (errcheck, gosimple, govet, ineffassign, staticcheck, unused)
• Updates code to satisfy linter requirements by improving error handling and adding package documentation
• Includes Makefile targets for running the linter and documentation in README.md

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
.golangci.yml	New linter configuration file with timeout and enabled linters
Makefile	Adds lint and lint-fix targets with updated PHONY declaration
README.md	Documents linter installation and usage instructions
internal/server/http.go	Removes trailing whitespace
internal/server/handlers.go	Adds package comment and improves error handling with proper defer patterns
internal/server/handlers_test.go	Reorders struct fields alphabetically
internal/providers/openai/openai.go	Adds package comment, reorders fields, and improves error handling with nolint directives
internal/core/types.go	Reorders struct fields alphabetically
internal/core/interfaces.go	Adds package documentation comment
config/config.go	Adds package comment and nolint directive for intentionally ignored error
cmd/gomodel/main.go	Adds package documentation comment
config/failover.yaml	Adds commented placeholder for future failover configuration

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[Copilot]

Using $(shell go env GOPATH) in the recipe itself may not work as expected. Consider using golangci-lint directly (assuming it's in PATH) or using a variable:

GOPATH ?= $(shell go env GOPATH)
lint-fix:
	$(GOPATH)/bin/golangci-lint run --fix ./...

Alternatively, just use golangci-lint run --fix ./... if it's expected to be in PATH after installation.

Suggested change

	$(shell go env GOPATH)/bin/golangci-lint run ./...
	# Run linter with auto-fix
	lint-fix:
	$(shell go env GOPATH)/bin/golangci-lint run --fix ./...
	golangci-lint run ./...
	# Run linter with auto-fix
	lint-fix:
	golangci-lint run --fix ./...

[Copilot]

The comment indicates that the error should be logged, but the code doesn't actually log it. Consider adding actual logging:

if _, err := io.Copy(c.Response().Writer, stream); err != nil {
    // Can't return error after headers are sent, log it
    // TODO: Add proper logging (e.g., log.Error(err))
    return nil
}

Or if logging isn't implemented yet, the comment should reflect the current behavior.

Suggested change

	// Can't return error after headers are sent, log it
	// Can't return error after headers are sent, so log it
	c.Logger().Error(err)

[Copilot]

The model name "gpt-5" doesn't exist. As of now, GPT-4 is the latest major version. Consider using an actual model name in the placeholder example (e.g., "gpt-4o-mini" or "gpt-4").

Suggested change

	# "gpt-5": [gemini3-pro, gemini2.5-pro]
	# "gpt-4": [gemini3-pro, gemini2.5-pro]