feat: add pathOverrides support for Envied annotations

[techouse]

Summary

• Add pathOverrides builder option for per-@Envied path overrides.
• Keep existing global path override behavior unchanged.
• Resolve override paths by @Envied(name) first, then original annotation path, then global path, then annotation/default path.
• Document YAML and CLI usage for pathOverrides.

Addresses

• Controlling Multiple Environments from the CLI? #169

[Copilot]

Pull request overview

Adds per-@Envied path override support to envied_generator via a new pathOverrides build option, while preserving existing global path override behavior and documenting configuration usage.

Changes:

• Introduces BuildOptions.pathOverrides and parsing/validation from builder config.
• Updates EnviedGenerator path resolution to prefer overrides by @Envied(name) then original @Envied(path), with fallback to global path then annotation/default.
• Adds generator and build options tests plus fixture .env files; updates README docs with YAML/CLI examples.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/envied_generator/lib/src/generator.dart	Implements path resolution precedence and updates generated_from to reflect resolved paths.
packages/envied_generator/lib/src/build_options.dart	Adds pathOverrides option and strict parsing/validation.
packages/envied_generator/test/envy_generator_test.dart	Registers new annotated-element tests covering override precedence and override disabled behavior.
packages/envied_generator/test/src/generator_tests_with_path_overrides.dart	Adds golden generation expectations for name/path/global fallback precedence.
packages/envied_generator/test/src/generator_tests_with_path_overrides_disabled.dart	Verifies pathOverrides are ignored when override: false.
packages/envied_generator/test/build_options_test.dart	Unit tests for pathOverrides parsing and invalid inputs.
packages/envied_generator/test/.env.path_overrides_*	Test env fixtures to validate override selection.
packages/envied/README.md	Documents pathOverrides in build.yaml and CLI usage, including precedence rules.

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