Agent task: harden standards spine to M3 readiness

[mdheller]

Agent-directed work package.

Target agent: GitHub Copilot coding agent, or Codex if Agent HQ is enabled for this repo.

Context:
This repository is the canonical standards spine for functional model surfaces. Main now contains README.md, repo.maturity.yaml, schemas/repo-maturity.schema.json, schemas/functional-service.schema.json, examples, tools, requirements.txt, Makefile, and .github/workflows/validate.yml.

Scope:

1. Inspect the current repository state before editing.
2. Make make validate pass locally and in GitHub Actions.
3. Add negative fixtures for invalid functional service manifests and invalid maturity records.
4. Add docs/MATURITY_MODEL.md explaining M0-M5, evidence requirements, and how Sociosphere/workspace-inventory should ingest maturity records.
5. Add docs/LAB_TEMPLATE.md describing the required lab repo skeleton and emitted functional-service.v1 manifest.
6. Keep this repo as standards-only. Do not add model weights, datasets, runtime secrets, or SourceOS image state.

Acceptance criteria:

• make validate passes.
• CI validates JSON schemas, examples, and repo.maturity.yaml.
• Negative fixtures are tested and fail for the expected reason.
• Documentation clearly distinguishes standards, lab outputs, runtime promotion, governance, and SourceOS carry-only references.

Validation commands:

python -m pip install -r requirements.txt
make validate

Boundary:
One PR only. Do not touch unrelated repos from this task.

[mdheller]

@copilot Please take this issue as the standards-spine hardening task.

Important execution rules:

• Inspect the live repository before editing; do not rely only on the issue description.
• Work in one PR from a copilot/... branch.
• Keep this repository standards-only: no model weights, datasets, runtime secrets, or SourceOS image state.
• Do not modify unrelated repositories.
• Make make validate pass and include negative fixtures for invalid maturity and functional-service manifests.

Acceptance criteria are in the issue body. The expected validation command is:

python -m pip install -r requirements.txt
make validate

When the PR is open, include a short evidence note in the PR body showing what was validated.