chore: move heavy verification to GitHub

[kaikisegfault]

Outcome

• make GitHub-hosted runners the default for builds, compiler/sanitizer matrices, fuzzing, simulations, packaging, and other heavy gates
• keep local work lightweight and targeted; forbid detached local repository processes and persistent check watchers
• cancel superseded workflow runs and cap each remote matrix job at 20 minutes
• require process/run audits and artifact cleanup at every completed phase
• add an idempotent narrow tools/clean-local.sh command for known reproducible build, toolchain, and Python cache paths
• persist the policy in AGENTS.md, both project execution skills, and engineering handoff guides

Lightweight local validation

• official skill validator: proceed-project valid
• official skill validator: verify-project valid
• cleanup command: shell syntax, executable mode, and repeated empty-state execution passed
• Python compileall, all shell syntax, JSON/TOML/YAML parsing, internal Markdown links, identity, and diff checks passed
• process and generated-directory audit: no repository workers/watchers or build/cache residue

Heavy validation

The GitHub-hosted four-preset matrix on this exact commit is the completion gate.