docs: standardize GitHub workflow and CI policy

[unityequilibrium]

Summary

• Standardize main, PR, branch, worktree, and checkpoint policy in AGENTS.md, CONTRIBUTING.md, and CONTEXT-MAP.md.
• Add the PR submission contract and daily repo-ops ledger entry.
• Replace the mixed legacy CI/deploy workflow with scoped PR validation, main validation, nightly research audit, and separate GitHub Pages workflows.
• Prune stale remote refs and remove only verified merged/superseded branches; retain unique superconductivity history as a local archive.

Validation

• Workflow YAML parsed successfully with the workspace PyYAML runtime.
• Python compile smoke test passed; existing SyntaxWarnings remain.
• cargo check --manifest-path services_and_experiments/uet_core/Cargo.toml --all-targets passed with existing warnings.
• Research baseline recorded in WORK_LEDGER: one legacy collection path error plus five artifact/environment/hash mismatches. Full research checks remain visible and are not allowlisted.

Scope

• No raw/private assets added.
• Actions do not commit or push source changes automatically.
• Platform deployment remains paused; GitHub Pages is separate.