docs: update CLAUDE.md testing requirements, architecture, and design system

- CLAUDE.md: add mandatory test coverage rule (all 3 layers required),
  document BYOB shop-aware S3 methods, update test count to 712
- architecture.md: mark MPS-14/15/16 complete, add environment/trial/BYOB
  to feature toggle matrix, add BYOB to S3 storage diagram
- design-system.md: add environment and trial banner components

CLAUDE.md

@@ -20,6 +20,13 @@ Files are NEVER streamed through uwsgi. The server only generates presigned URLs
 - **Uploads**: presigned `post` → client uploads directly to Spaces
 - **Thumbnails**: public CDN URLs with `?ts=` cache busting
 
+**BYOB (Bring Your Own Bucket)**: Shops can configure their own S3-compatible bucket (`bucket-settings` form section). When enabled, all presigned URLs and CDN references use the shop's bucket. Always use shop-aware request methods in views and templates:
+- `request.shop_uploads_client` — S3 client (shop's or MPS default)
+- `request.shop_bucket_name` — bucket name (shop's or MPS default)
+- `request.shop_cdn_endpoint` — CDN URL (shop's or MPS default)
+
+**NEVER** use `request.app["bucket.secure_uploads"]`, `request.app["bucket.secure_uploads.get_endpoint"]`, or `request.secure_uploads_client` directly in views or templates. These are only used internally by `request_methods.py` as fallbacks.
+
 ### Karaoke Pipeline (lib/karaoke.py)
 
 Disk-backed vocal isolation pipeline. Downloads media from S3, builds a JSON
@@ -100,10 +107,12 @@ env/bin/py.test make_post_sell/tests/test_functional.py  # Functional tests
 env/bin/py.test --cov=make_post_sell.models.cart --cov-report=term-missing make_post_sell/tests/test_models.py::TestCart
 ```
 
-### Current Coverage
+### Current Coverage (712 tests)
 - Cart model unit tests cover critical business logic like `requires_payment` threshold (64 cents)
-- Integration tests verify the original AttributeError defect fix for free coupon checkout
-- Functional tests provide end-to-end coverage of cart/checkout/payment flows
+- Shop environment, trial, and BYOB model properties (TestShopEnvironment, TestShopTrial, TestShopBYOB)
+- Gift card model unit tests (generation, validation, transactions)
+- Integration tests verify free coupon checkout, gift card flows, and multi-model interactions
+- Functional tests cover cart/checkout/payment, gift card settings, environment settings, bucket settings
 
 ## Database Location
 
@@ -260,6 +269,13 @@ Elements that must stay in sync: CTA edit button, download button, comment form
 
 Disabling or removing tests weakens the codebase and is unacceptable. Tests are critical safety nets that prevent regressions.
 
+**MANDATORY TEST COVERAGE**: Every new feature, model property, view handler, or form section MUST have tests across all three layers:
+- **Unit tests** (`test_models.py`) — Test new model properties, methods, and business logic in isolation using `mock.patch`. No DB required.
+- **Integration tests** (`test_integration.py`) — Test interactions between models, especially multi-model workflows (e.g., cart + coupon + gift card).
+- **Functional tests** (`test_functional.py`) — Test through the web interface using `webtest.TestApp`. Cover settings form POSTs, page loads, flash messages, and DB state changes.
+
+If a feature touches all three layers (model + view + template), it needs tests in all three files. No exceptions. Untested code is incomplete code.
+
 **AUTO-PUSH**: When you write new tests to cover new code paths and the full test suite passes, commit and push without asking. Bump GIT_HASH after pushing.
 
 ## Post-Work Chores