fix(governance): make generated bumps warning-clean

[Malakof]

Context

The first v1.4.0 consumer bump proved the deterministic type mapping, but raw format-check logs exposed two remaining generator defects: the automated PR body lacked governed sections, and kernel-label provenance remained a qualitative LLM task. The model therefore emitted a false kernel-label warning even though the PR had no kernel labels.

Acceptance criteria

• generated bump PR bodies include Context, Acceptance criteria, Out of scope, and Validation
• author and kernel-label provenance are computed deterministically
• the LLM is not asked to infer mechanical kernel-label facts
• human-applied kernel labels remain visible as deterministic warnings
• bot-applied kernel labels are distinguished explicitly
• v1.4.1 propagation creates a warning-clean crystal-capabilities bump PR

Out of scope

• suppressing or filtering model output
• weakening label or title checks
• product, dependency, test selector, retry, or timeout changes
• crystal-platform#332

Validation

• python3 -m py_compile scripts/*.py
• python3 -m unittest discover -s tests -v — 10 passed
• validate_title.py against crystal-capabilities#7 — pass
• validate_labels.py against crystal-capabilities#7 — pass
• git diff --check

Refs Malakof/crystal-platform#409.
Supersedes the warning-producing v1.4.0 bump behavior.