feat(perf): mobile performance Phase 1 — dequeue unused plugin assets + slim fonts + preconnect (#13)

Ships peptide-starter-theme v1.6.0.

Changes:
- New inc/perf-asset-policy.php module: conditional dequeue of WC/Elementor/USMI assets on pages that do not need them, Google Fonts weight slim (Roboto 100..900 → 400/500/700; Roboto Slab → 400/700), wp_resource_hints preconnect for fonts.googleapis.com + fonts.gstatic.com, cookie-notice-front script defer.
- Kill-switch constant PEPTIDE_STARTER_PERF_DEQUEUE (default true) for instant rollback via wp-config.php.
- 4 extensibility filters: peptide_starter_perf_woocommerce_{styles,scripts}, _elementor_{styles,scripts}, _usmi_{styles,scripts}, _font_weights.
- 13 unit tests in tests/test-perf-asset-policy.php.
- Bootstrap: 2 lines in functions.php (require + after_setup_theme action).
- Docs: CHANGELOG [1.6.0], ARCHITECTURE.md, CONVENTIONS.md how-to.

Target: mobile PSI 74 → 90+, LCP 5.4s → ~2.5s.

Post-deploy: purge LiteSpeed CSS bundle.

QA: qa-reviews/peptide-starter-theme/2026-04-23-a54b5c9.md (APPROVE with handle-drift verified false-positive).

style.css

@@ -4,7 +4,7 @@ Theme URI: https://github.com/peptiderepo/peptide-starter
 Description: Premium, accessible WordPress theme for scientific peptide reference database
 Author: Peptide Repo
 Author URI: https://peptiderepo.com
-Version: 1.5.2
+Version: 1.6.0
 License: GPL v2 or later
 License URI: https://www.gnu.org/licenses/gpl-2.0.html
 Text Domain: peptide-starter