feat: Create a fully working example for clarity

[MgnMtn]

Pull Request also address:

Resolves #1
Resolves #8
Resolves #10

[Copilot]

Pull request overview

This PR makes multiplex easier to understand and run end-to-end by (1) validating/reading only the prompt keys needed for the selected mutation approach, (2) fixing and testing the Maven execution backend, and (3) bundling a self-contained runnable example project/config with accompanying documentation.

Changes:

• Add multiplex/prompts.py (resolve_prompts) and switch __main__.py to validate only the selected approach’s required system_prompts keys (addresses issue #1 / PR #10).
• Rework multiplex/execute/maven.py to follow the same evaluation flow as defects4j.py, plus add unit tests for the Maven backend (addresses issue #8).
• Add a bundled Maven example project + config and update docs/README to point users at uv run multiplex ./examples/config.yml.

Reviewed changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/test_prompts.py	Adds tests asserting prompt resolution only requires the selected approach’s keys and fails fast with actionable errors.
tests/execute/test_maven.py	Adds unit tests covering Maven backend execution mapping and mutant loop behavior (summary writing, baseline failure, skip non-compilable).
tests/execute/conftest.py	Adds runtime-style import setup for execution backend tests by prepending multiplex/ to sys.path.
README.md	Fixes token_env_var example key and documents how to run the bundled example.
multiplex/prompts.py	Introduces approach→prompt-key mapping and resolve_prompts validation/selection logic.
multiplex/execute/maven.py	Rewrites Maven backend to baseline first, classify mutants, and write mutant_summary.csv.
multiplex/main.py	Uses resolve_prompts early and simplifies approach dispatch using the validated approach variable.
examples/README.md	Documents the bundled end-to-end example workflow, prerequisites, and outputs.
examples/project/example/src/test/java/com/example/ClassifierTest.java	Adds JUnit tests for the example project to enable mutation killing/survival demonstration.
examples/project/example/src/main/java/com/example/Classifier.java	Adds a small example class/method as the mutation target.
examples/project/example/pom.xml	Adds a minimal Maven project definition (Java 17 + JUnit 5).
examples/config.yml	Adds a runnable example configuration and includes prompt blocks (only selected approach required).
docs/MODULE_REFERENCE.md	Documents the new prompts.py module and updates Maven backend reference.
docs/EXTENDING.md	Updates approach-extension instructions to use APPROACH_PROMPT_KEYS / resolve_prompts.
docs/DEVELOPMENT.md	Adds example-run docs and updates known-issues notes reflecting fixed prompt handling and Maven backend.
docs/CONFIG.md	Updates config semantics to “per-approach required prompts” and clarifies failure modes.
docs/ARCHITECTURE.md	Updates the Maven backend description to reflect the now-functional behavior and example usage.
CLAUDE.md	Updates repository conventions/docs to match the new prompt resolution flow and bundled example.
AGENTS.md	Updates the agent guidance to reflect new prompt resolution and example run.
.gitignore	Ignores run artifacts like output/ and *.orig backups created during runs.
.github/copilot-instructions.md	Adds repository-specific Copilot guidance matching the updated conventions and example.

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