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>

shopdb/core/api/settings.py

@@ -466,6 +466,27 @@ def build_default_settings():
             'category': 'branding',
             'description': 'Primary brand color as a CSS color value (blank = built-in theme color)'
         },
+        {
+            'key': 'brand_primary_dark_color',
+            'value': '',
+            'valuetype': 'string',
+            'category': 'branding',
+            'description': 'Primary hover/active color (blank = derived by darkening the primary color ~15%)'
+        },
+        {
+            'key': 'brand_accent_color',
+            'value': '',
+            'valuetype': 'string',
+            'category': 'branding',
+            'description': 'Accent color for secondary buttons and badges (blank = built-in theme color)'
+        },
+        {
+            'key': 'brand_sidebar_color',
+            'value': '',
+            'valuetype': 'string',
+            'category': 'branding',
+            'description': 'Sidebar background color (blank = built-in theme color)'
+        },
     ]
 
     # Printed QR/label targets. Blank template = QR links to the asset's own