Automate proof script: add JBang CI runner for proof/ scripts

[Copilot]

No automated way existed to run all the proof scripts in the proof/ directory to verify they compile and execute correctly. This adds a JBang runner script and a GitHub Actions workflow as a CI gate for all proof scripts.

New: html-generators/proof.java

JBang script (Java 25) that:

• Walks proof/**/*.java for all standalone JBang proof scripts
• Runs each via jbang --quiet <file>, checking the exit code
• Reports per-script OK/FAILED/TIMEOUT, exits 1 on any failure
• --list flag lists all proof scripts

New: proof/ directory (105 scripts)

One JBang script per pattern (//JAVA 25+), organized by category mirroring content/:

proof/language/TypeInferenceWithVar.java
proof/collections/ImmutableListCreation.java
proof/streams/StreamTolist.java
...

Each script has a /// Proof: slug-name header and demonstrates the modern approach from the corresponding content YAML file.

New: .github/workflows/proof.yml

Runs jbang html-generators/proof.java on push/PR when proof/** changes, using Java 25 + JBang.

Supporting changes

• CONTRIBUTING.md: Added step to create a proof script when adding a new pattern
• html-generators/README.md: Added proof.java to the files table and documented the proof.yml workflow
• .github/copilot-instructions.md: Added proof/ to the project structure and documented the proof script convention

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Feature] Automate proof script</issue_title>
<issue_description>### Describe the feature

We now have proof but we don't have a way to run all of them to verify all of them work.

Why would this be useful?

No response

Alternatives considered

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature] Automate proof script #112

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[brunoborges]

@copilot you completely missed the proof folder that already contains java code!

[Copilot]

@copilot you completely missed the proof folder that already contains java code!

Fixed in commit 2564051. The proof/ directory with 105 existing JBang scripts was brought in and html-generators/proof.java was rewritten to run all proof/**/*.java files via jbang. The workflow now triggers on proof/** changes. I also reverted the YAML proofCode additions that were incorrect.

[brunoborges]

@copilot this PR should be targeting the slug-proof branch, which already contains the proof folder

[Copilot]

@copilot this PR should be targeting the slug-proof branch, which already contains the proof folder

Changing a PR's base branch requires action in the GitHub UI — I can't do that directly. To retarget this PR:

1. Open the PR on GitHub
2. Click Edit next to the PR title
3. Change the base dropdown from main to copilot/implement-proof-for-slugs

Once the base is changed, the 105 proof/**/*.java files will disappear from the diff (since they already exist in that branch), leaving only the meaningful additions: html-generators/proof.java, .github/workflows/proof.yml, and the documentation updates.