refactor(linting): apply golangci-lint fixes across codebase

[flexiondotorg]

Summary

Apply automated linting fixes across the codebase to ensure code quality and consistency standards.

Changes

• Add .golangci.yml configuration for static analysis
• Fix linting errors in audio processing pipeline (analyzer, decoder, FFT, buffer management)
• Fix linting errors in encoder and video rendering logic
• Fix linting errors in CLI help and progress UI components
• Update build workflows and configuration files
• Add GitHub community health files (FUNDING, templates, workflows)
• Update flake configuration for environment setup
• Update justfile with additional development targets

Testing

Code linting validated against .golangci.yml configuration; all identified issues resolved.

[cubic-dev-ai]

No issues found across 48 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Requires human review: Large-scale refactor across 48 files, including type renames, CI/CD workflow changes, and modifications to core audio/video processing logic which require human validation.}