USB label batch: brand colors + print-color-adjust; document migration strategy

- USBLabelBatch.vue: recolor controls/selection/cell borders to the app CSS
  variables (was hardcoded #667eea/#28a745/#dc3545) and add
  `print-color-adjust: exact` so barcodes print even with "Background graphics"
  off. (Barcodes render as vector SVG, so no canvas->img change needed.)
- ADR-004: document the resolved migration strategy - single core Alembic chain
  (`flask db upgrade`), bundled plugin schema folded into core (7c04), resolving
  the Phase 7B per-plugin-chain conflict footgun. External plugins may still
  ship their own chains.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/adr/ADR-004-deployment-topology.md

@@ -56,6 +56,19 @@ The framework provides:
 1. **Multi-tenant single instance.** Lower operational overhead at scale, easier cross-site reporting, but adds significant code complexity and risk: every query needs a tenant filter, auth gets complex, schema migrations affect every site at once, and a bug at one site can leak data across sites. Rejected for v1; revisit if and only if more than five sites adopt and operational overhead becomes painful.
 2. **Hybrid: per-site DB but central app server.** Adds the operational complexity of multi-tenancy without isolating the failure domain (one app crash = all sites down). Rejected.
 
+## Migration strategy (resolved)
+
+Deploys run a single core Alembic chain: `flask db upgrade`. Bundled plugins do
+NOT carry their own migration chains - their tables are folded into the core
+chain (migration `7c04_fold_plugin_schema`). This was a deliberate resolution of
+the Phase 7B footgun where bundled-plugin baselines and the core baseline both
+created the same tables, so `flask plugin upgrade-all` would conflict. A fresh
+`flask db upgrade` reproduces the live schema exactly (verified on a scratch DB).
+
+External (out-of-tree) plugins per ADR-003 may still ship their own migrations;
+the framework supports per-plugin chains for them. Only the in-tree bundled
+plugins are consolidated into core.
+
 ## Open questions
 
 - Should the framework provide an optional **read-only fleet roll-up** mode where a "central" instance can pull aggregate metrics from each site's API? Defer. Out of scope for v1.