Re-add spec-alignment + capability-validation as required checks (#39 drifted)

## Summary

#39 asked to add `spec-alignment` and `capability-validation` as required checks and was closed completed (decision-log 28). The live ruleset `traverse-governance-required-checks` (id 18597008) still only requires:

- `cla / cla`
- `baseline / governance-baseline`

Confirmed 2026-09-14 while reviewing how #487 merged. PR #487's `capability-validation` was green; it could have merged even if that job had failed. Post-merge `push` CV going red is a different (signature) issue; this ticket is only the ruleset drift.

This still conflicts with spec 001 SC-002.

Decided in the 2026-09-14 first-contributor-publish brainstorm (decision-log entry 113): honor decision 28 — require those two contexts. Do **not** add a required human review count (review-count stays 0).

## Ask (owner action — rulesets are owner-controlled)

On `traverse-governance-required-checks` for `main`, add:

- `spec-alignment`
- `capability-validation`

Leave `cla / cla` and `baseline / governance-baseline` in place.

## Why now

Outside contributors are on the one-PR publish path (#485, #488, #489, #492). CLA + baseline alone is not enough once 1.0.0 is immutable.

## Labels

`no-spec-needed` · `needs-enrico`

Start with the GitHub ruleset `traverse-governance-required-checks` (id 18597008) for `main` and compare its required checks with spec 001 SC-002 and decision-log entries 28 and 113. Done means adding `spec-alignment` and `capability-validation` while retaining `cla / cla` and `baseline / governance-baseline`, with review-count still 0.

Written by the indexing model from the issue text.