Add config file loading with startup defaults and CLI override semantics

[Copilot]

Configuration supported JSON persistence via Save but had no complementary read path, forcing full flag specification on every run. This change introduces config file loading and wires default file discovery into startup so persisted values are applied before flags are parsed.

• Configuration read support

  • Added (*Configuration).Load(path string) error to read JSON from disk and unmarshal into the active config struct.
  • Returns contextual errors for read and unmarshal failures.

• Default config discovery

  • Added (*Configuration).LoadDefault() error to attempt, in order:
    1. redeye.json (working directory)
    2. ~/.redeye.json (user home)
  • Loads the first existing file; skips missing files cleanly.

• Startup integration (flag precedence preserved)

  • main() now calls config.LoadDefault() before flag.Parse(), so file-backed defaults are loaded first and explicit CLI flags continue to win.

func main() {
    if err := config.LoadDefault(); err != nil {
        log.Fatalf("failed to load default config: %+v", err)
    }
    flag.Parse()
}

[Copilot]

Pull request overview

This PR adds a missing “read” path for persisted configuration by introducing JSON config file loading, default config file discovery, and startup wiring so file-backed values are applied before CLI flag parsing (keeping explicit CLI flags as the highest precedence).

Changes:

• Added (*Configuration).Load(path string) and (*Configuration).LoadDefault() to load JSON config from disk (with default path discovery).
• Updated main() to call config.LoadDefault() before flag.Parse() so persisted values apply as defaults.
• Added unit tests for config loading and default-file fallback behavior.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
redeye/main.go	Loads default config files before parsing flags to apply persisted defaults at startup.
config.go	Implements Load and LoadDefault for JSON config reading and default path discovery.
config_test.go	Adds tests covering Load success/read errors and LoadDefault selection order.
go.mod	Tidies module requirements formatting/order.
go.sum	Updates checksums for added/transitive dependencies after module tidying.

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