feat: close stub-page gaps - profile login/logout, admin Reports/Settings, Help/Docs links

Sprint A: storefront header profile control (login/logout only, no menu),
wired to existing customer Telegram auth (AuthService).

Sprint B: backoffice/reports page, reuses AdminAnalyticsFacade (Sales,
Top Products, Marketplace Health cards + CSV export).

Sprint C: backoffice/settings page, admin UI density preference
(comfortable/compact), localStorage-persisted, applied to app-table
across all admin list pages.

Sprint D: admin bottom-nav Help -> mailto using existing supportEmail,
Documentation -> external link via new TenantConfig.documentationUrl.
AdminNavLink gains externalHref for non-routerLink nav entries.

Docs: docs/GLOBAL-SPRINT-PLAN.md tracks the full sprint breakdown.
docs/COMING-SOON-AUDIT.md removed, folded into docs/KNOWN-ISSUES.md.
docs/BACKEND.md updated with the new documentationUrl bootstrap field.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/BACKEND.md

@@ -168,8 +168,12 @@ Each nested field, with its source model file under
 - **`tenant`** (`TenantConfig`, `tenant.model.ts`) —
   `{ id (UUID), slug, code, host, name, websiteBaseUrl, builderBaseUrl,
   backofficeBaseUrl, defaultLocale, supportedLocales[], defaultCurrency,
-  supportedCurrencies[], timezone }`. Identifies the tenant and its per-surface
-  base URLs, locale/currency sets, and timezone.
+  supportedCurrencies[], timezone, documentationUrl? }`. Identifies the tenant
+  and its per-surface base URLs, locale/currency sets, and timezone.
+  `documentationUrl` (optional string) is the external docs link rendered by
+  the backoffice "Documentation" nav item — when absent, that nav item shows
+  as a disabled `comingSoon` entry instead of a link (frontend-only fallback,
+  no backend action required beyond optionally sending the field).
 - **`branding`** (`BrandingConfig`, `branding.model.ts`) —
   `{ brandName, legalName, slogan?, logoUrl, logoCompactUrl?, faviconUrl,
   appIconUrl?, socialImageUrl?, galleryUrls?, supportEmail?, supportPhone? }`.
@@ -304,7 +308,8 @@ trimmed for length; full versions in that file):
     "supportedLocales": ["ru", "en", "hy"],
     "defaultCurrency": "RUB",
     "supportedCurrencies": ["RUB", "USD", "EUR", "AMD"],
-    "timezone": "Europe/Moscow"
+    "timezone": "Europe/Moscow",
+    "documentationUrl": "https://docs.marketplace.local"
   },
   "branding": {
     "brandName": "Marketplace",