Plugin framework maturation, reports overhaul, theming, and USB frontend repair

Framework:
- Per-plugin Alembic migration chains (ADR-008): every bundled plugin
  carries its own chain with a stamp-only anchor at the ownership cutover;
  new plugin schema lands in plugins/<name>/migrations/, never the core
  chain. Deploys add flask plugin upgrade-all. Fixed a latent bug in the
  shared alembic template (engine URL resolution) and taught the metadata
  filter to include FK-referenced core tables.
- Frontend plugin route gating (ADR-009): plugin routes carry meta.plugin;
  a disabled plugin's pages redirect to the dashboard via a cached,
  fail-open check against the new public GET /api/plugins/enabled.
- get_reports() plugin hook (contract 0.5.0 -> 0.6.0): plugins contribute
  report cards; warranty and toner cards moved off the hardcoded list.

Reports:
- Hub grouped by category with search; inline reports render at the top,
  are URL-backed (?report=id, back-button and deep links work), expose
  their server-side filter params as controls, and export CSV. Warranty
  and Toner pages gained CSV export.
- Deleted the dead legacy Warranty Status report (always-zero buckets
  from a retired column).

Theming and fonts:
- Inter (variable) bundled locally via @fontsource, replacing the Google
  Fonts Roboto import - air-gapped installs now render correctly; tables
  use tabular numerals.
- Optional brand_primary_dark_color, brand_accent_color,
  brand_sidebar_color settings applied to CSS vars at bootstrap.

USB frontend repair (views were reading a dead legacy shape):
- List/detail/form and the employee profile USB panels remapped to the
  real API shape (device_id/device_desc/checkinoutlog); employee panels
  now use /usb/checkouts endpoints; external-mode /usb/checkouts/active
  honors the badge filter; dead client methods pruned.

Also: warranties list page no longer requires login (matches app
convention); collector doc rewritten with a GE-Enforce integration guide
and paste-ready PowerShell reporter; ADR index and CHANGELOG updated.

Verified: 323 tests pass, naming/style green, frontend builds, plugin
migration dry-run green on scratch MySQL.

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

frontend/src/views/AppLayout.vue

@@ -87,7 +87,7 @@ import { useRouter } from 'vue-router'
 import ToastHost from '../components/ToastHost.vue'
 import {
   Sun, Moon, LayoutDashboard, Calendar, Map, Cog, Monitor,
-  Printer, Globe, Usb, AppWindow, BookOpen, BarChart3, Bell, Image, ShieldCheck
+  Printer, Globe, Usb, AppWindow, BookOpen, BarChart3, Bell, Image, ShieldCheck, Ruler
 } from 'lucide-vue-next'
 import { useAuthStore } from '../stores/auth'
 import { currentTheme, toggleTheme } from '../stores/theme'
@@ -127,6 +127,7 @@ const iconMap = {
   'bar-chart-3': BarChart3,
   'image': Image,
   'shield': ShieldCheck,
+  'ruler': Ruler,
 }
 
 // Default navigation (used as fallback if API fails)