[Feature]: Use standard config file naming

Description

I see there’s already an issue about using a .env file for local config, and a PR that renames it to .opencommit.env.

However, this naming does not follow common Node.js config file conventions.

Examples of standard config file names:

• ESLint: .eslintrc / eslint.config.js
• Prettier: .prettierrc
• Stylelint: .stylelintrc
• Jest: jest.config.js

Suggested Solution

Use a config loader like cosmiconfig, which supports popular formats like .opencommitrc, opencommit.config.js, etc.

By default, Cosmiconfig will check the current directory for the following:

• a package.json property
• a JSON or YAML, extensionless "rc file"
• an "rc file" with the extensions .json, .yaml, .yml, .js, .ts, .mjs, or .cjs
• any of the above two inside a .config subdirectory
• a .config.js, .config.ts, .config.mjs, or .config.cjs file

This would:

• Follow standard naming
• Simplify config handling (loading, merging configs, etc.)
• Allow removal of custom logic:
  https://github.com/di-sukharev/opencommit/blob/c1756b85aff7804b194d41cc9e5bde32c73fe22f/src/commands/config.ts#L919-L931

Happy to help if needed!

Alternatives

No response

Additional Context

No response

Start with the custom configuration logic in src/commands/config.ts, especially lines 919-931, and review the related issue 305 and PR 480. Evaluate how a cosmiconfig-based loader would handle the proposed standard names and formats, including loading and merging configuration. Done means the supported standard naming conventions work and the custom logic can be removed where appropriate.