Expose docs bootstrap contracts

[chubes4]

Summary

• Add a bootstrap_contract JSON input to maintain-docs.yml, normalize it during prepare, render it into bootstrap prompts as success criteria, and pass it through as post_run_workspace_checks.
• Teach technical and user bootstrap prompts that caller-declared contracts are required completion criteria, including no_changes semantics.
• Extend bundle validation to assert complete bootstrap contract semantics and reject deferred/backlog language.

Issue

• Fixes Expose deterministic docs bootstrap contract inputs #91.

Dependency

• Depends on Add post-run workspace contract checks for agent CI Extra-Chill/homeboy-extensions#1314 for the reusable runner to accept and enforce the intended post_run_workspace_checks JSON input.
• Until that generic runner support lands, consumers should treat this Docs Agent wiring as the contract-side implementation.

Verification

• jq empty bundles/technical-docs-agent/flows/technical-docs-bootstrap-flow.json bundles/user-docs-agent/flows/user-docs-bootstrap-flow.json bundles/technical-docs-agent/pipelines/technical-docs-pipeline.json bundles/user-docs-agent/pipelines/user-docs-pipeline.json tests/docs-agent.validate-bundle-spec.json tests/technical-docs-agent.validate-bundle-spec.json tests/user-docs-agent.validate-bundle-spec.json
• php tests/validate-docs-agent-bundle.php
• php tests/repair-docs-links-smoke.php

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Implemented the workflow contract plumbing, prompt updates, validation assertions, and local verification; Chris remains responsible for review and merge.