ci: add task schema validation workflow for pull requests

[okwn]

Summary

• Add .github/workflows/validate-task-schema.yml that validates task directory structure on PRs touching task directories
• Checks: README.md exists with Status field, Makefile with standard includes, foundry.toml, script/ with .sol files, FACILITATOR.md, .env, validations/, records/

Problem

There is no automated check that new task directories follow the conventions documented in AGENTS.md. Tasks can be submitted with missing files (e.g., no FACILITATOR.md, no Makefile includes, no Status field in README).

Solution

A lightweight GitHub Actions workflow that runs on PRs touching any task directory (mainnet/, sepolia/, sepolia-alpha/, zeronet/). It validates the schema without modifying any artifacts.

Tests

• Validated against existing tasks locally — checks README Status field, Makefile includes, foundry.toml, script/ .sol count, FACILITATOR.md existence, .env, validations/, records/
• Uses git diff to detect only changed tasks — no false positives on unrelated changes

Risk / Compatibility

• Risk: VERY LOW
• Affects: CI configuration only; no production artifact changes
• Read-only validation of directory structure
• Does not block merged tasks (Status: EXECUTED) — only checks conventions are followed

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 2 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 2 2 1 if commit is unverified 1 Sum 3