refactor: migrate templates and static files to self-contained modules

Templates Migration:
- Migrate admin templates to modules (tenancy, billing, monitoring, marketplace, etc.)
- Migrate vendor templates to modules (tenancy, billing, orders, messaging, etc.)
- Migrate storefront templates to modules (catalog, customers, orders, cart, checkout, cms)
- Migrate public templates to modules (billing, marketplace, cms)
- Keep shared templates in app/templates/ (base.html, errors/, partials/, macros/)
- Migrate letzshop partials to marketplace module

Static Files Migration:
- Migrate admin JS to modules: tenancy (23 files), core (5 files), monitoring (1 file)
- Migrate vendor JS to modules: tenancy (4 files), core (2 files)
- Migrate shared JS: vendor-selector.js to core, media-picker.js to cms
- Migrate storefront JS: storefront-layout.js to core
- Keep framework JS in static/ (api-client, utils, money, icons, log-config, lib/)
- Update all template references to use module_static paths

Naming Consistency:
- Rename static/platform/ to static/public/
- Rename app/templates/platform/ to app/templates/public/
- Update all extends and static references

Documentation:
- Update module-system.md with shared templates documentation
- Update frontend-structure.md with new module JS organization

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/v1/platform/__init__.py

@@ -1,22 +0,0 @@
-# app/api/v1/platform/__init__.py
-"""
-Platform public API endpoints.
-
-These endpoints are publicly accessible (no authentication required)
-and serve the marketing homepage, pricing pages, and signup flows.
-"""
-
-from fastapi import APIRouter
-
-from app.api.v1.platform import pricing, letzshop_vendors, signup
-
-router = APIRouter()
-
-# Public pricing and tier info
-router.include_router(pricing.router, tags=["platform-pricing"])
-
-# Letzshop vendor lookup
-router.include_router(letzshop_vendors.router, tags=["platform-vendors"])
-
-# Signup flow
-router.include_router(signup.router, tags=["platform-signup"])