docs: add platform vision ADR and Sprint 16 project editor design spec

Records the multi-tenant marketplace platform architecture as ADR-0001
(bootstrap-driven, config-only frontend) with a source-backed fact pack,
and writes the approved Sprint 16 design for extending the existing
project editor with Languages/Navigation tabs, an HTML editor, and a
client-side draft/publish flow.

docs/context/adrs/ADR-0001-marketplace-platform-vision.md

@@ -0,0 +1,67 @@
+---
+id: ADR-0001
+title: Multi-tenant marketplace platform vision and config-driven architecture
+status: active
+date: 2026-07-13
+tags: ["architecture", "philosophy", "multi-tenant", "bootstrap"]
+---
+
+## Context
+
+This is not a single marketplace — it is a multi-tenant platform powering unlimited
+marketplaces (e.g. electronics.example.com, books.example.com) from one codebase.
+Every marketplace is configured from the backend via a bootstrap configuration
+(`GET /bootstrap`). No marketplace-specific code may exist in the frontend.
+
+## Decision
+
+- The frontend (Angular 20, standalone components, Signals, RxJS, SCSS) is a pure
+  renderer. It owns render, navigation, interaction, validation, animations only.
+- The backend (ASP.NET Core REST API) owns branding, pages, layouts, languages,
+  homepage, navigation, categories, products, footer, static pages, payment
+  configuration, and enabled features.
+- Flow: Bootstrap → Runtime Provider → Configuration Store → Renderer → Widgets.
+  Nothing depends on build-time environments; everything depends on runtime
+  configuration.
+- Bootstrap contains only data needed before the app starts (name, logo, colors,
+  languages, footer pages, homepage layout, navigation, enabled widgets). It must
+  never contain products, orders, cart, or users.
+- Widgets never own page spacing — only their own internal layout. The renderer
+  owns sections, spacing, and page width.
+- Homepage is composed from a configurable, ordered list of sections (Section
+  Engine): Hero, Categories, Featured Products, Banner, Latest Products, Custom
+  HTML, Newsletter, etc.
+- All layouts (homepage, PLP, etc.) must be backend-configurable without frontend
+  changes.
+- All user-facing text is translatable via a `translations.{lang}` shape, not a
+  flat `title` field. Adding/removing a supported language must automatically
+  expose/remove translation fields across all translatable objects, generically —
+  never per-field hardcoding.
+- Static pages (About Us, Privacy, Terms, Contacts, Return Policy, Delivery,
+  custom pages) are backend-delivered HTML, multilingual, and drive the footer.
+- Admin and storefront share a domain but are fully separate applications: the
+  marketplace bundle never ships admin code and vice versa. Bootstrap is public;
+  Admin is protected by JWT + roles/permissions + tenant isolation (Super Admin,
+  Marketplace Admin, Moderator, Editor, Support, Customer).
+
+## Coding rules
+
+- Never hardcode marketplace data or introduce marketplace-specific conditionals.
+- Never use environment flags to drive UI — everything is config-driven.
+- Keep components small; prefer composition and reusable widgets; never
+  duplicate layouts.
+- Business logic lives in services/facades, not components.
+- Prefer Signals and standalone components.
+- Every new feature ships with docs: frontend docs, backend contract, bootstrap
+  updates, API examples, migration notes if needed.
+
+## Guiding question
+
+Before implementing anything: "Will this still make sense after 50 marketplaces
+and 100 developers?" If not, redesign before coding.
+
+## Consequences
+
+Any feature (including the Sprint 16 Project Editor) must edit the same Bootstrap
+model the storefront consumes — no parallel/duplicate configuration models are
+permitted anywhere in the platform.