feat(cpt): consolidate peptide CPT with PSA; drop pr_peptide (v0.2.0)

Resolves the rewrite slug collision that was 404'ing all 89 production
peptide detail pages. PR Core v0.1.1 registered an empty pr_peptide CPT
claiming /peptides/%postname%/; WP's rewrite resolver picked it over PSA's
populated peptide CPT. This release consolidates both registrations onto a
single peptide CPT owned by PR Core. PSA v4.5.0 drops its registration in
favor of this one.

## Contract (per CTO msg 02)
- POST_TYPE: pr_peptide -> peptide
- TAX_CATEGORY: pr_peptide_category -> peptide_category
- TAX_FAMILY const removed (pr_peptide_family was never populated)
- CPT + taxonomy registration guarded with post_type_exists() / taxonomy_exists()
  so deploy order between PR Core and PSA is forgiving
- Args harmonized as superset of PSA + prior PR Core (thumbnail added to
  supports; capability_type + map_meta_cap preserved)
- Activator: flush_rewrite_rules(false) on activation; new
  maybe_flush_on_version_change() handler hooked at init:999 for in-place
  updates that bypass the activation hook (e.g. SCP deploys)
- uninstall.php: blanket DELETE replaced with JOIN on _pr_core_authored so
  PSA-authored peptide posts (the 89 canonical monographs) are never destroyed;
  peptide_category terms preserved (shared ownership)
- Scrub scope: narrow — CPT-slug-derived identifiers only; class names,
  file names, PR_CORE_* constants, pr_core_* options, and pr-core/v1 REST
  namespace remain

## Docs
- ARCHITECTURE.md: new Key Decision #7 (v0.2.0 consolidation) and §2.9
  Uninstall specification
- CONVENTIONS.md: CPT Ownership rule + _pr_core_authored flag contract

## Tests
- Lightweight harness (tests/bootstrap.php) that stubs the handful of WP
  functions exercised by the CPT class
- tests/unit/test-peptide-cpt.php asserts: constants match contract,
  TAX_FAMILY is removed, guard no-ops when post_type_exists/taxonomy_exists
  returns true, args payload shape (thumbnail in supports, rewrite slug,
  REST namespace), hooks wired
- CI: new 'Unit tests (lightweight, no PHPUnit)' step in lint-php job,
  runs across PHP 8.1/8.2/8.3. Full PHPUnit + wp-env harness is a
  follow-up

Refs: convo/prcore/threads/2026-04-peptides-cpt-collision/02-cto-correction.md

includes/admin/class-pr-core-admin-columns.php

@@ -2,7 +2,7 @@
 declare(strict_types=1);
 
 /**
- * Custom admin list-table columns for the pr_peptide CPT.
+ * Custom admin list-table columns for the peptide CPT.
  *
  * What: Adds evidence strength, editorial status, and dosing count columns.
  * Who calls it: PR_Core_Admin via manage_posts_columns and custom_column hooks.