feat(inventory): printable PDF spool labels in 4 sizes (#809)

Closes the longest-standing inventory gap — finding a specific spool
  in a closet of 50 partials. Per-spool icon button on every inventory
  card and table row, plus a "Print labels..." header action that opens
  a multi-select picker pre-loaded with the currently filtered spools.

  Four pre-built templates: AMS holder (30 x 15 mm) for the popular
  Makerworld AMS Filament Label Holder, single box label (62 x 29 mm)
  for Brother PT/QL or Dymo small labels, Avery L7160 (A4, 21 per
  sheet), and Avery 5160 (US Letter, 30 per sheet). Each label carries
  the colour swatch (with multi-colour gradient stripes for spools
  with extra_colors set), brand, material, name, the *spool ID*
  (bsaunder's articulated user-need: telling 8 spools of "PLA White"
  apart, especially partials), and a QR code that deep-links to
  /inventory?spool=<id> for phone-scan round-trips. Box-label adds
  storage location; AMS-holder drops the QR — at 30 x 15 mm there is
  no room for swatch + text + QR without truncating away the spool ID,
  and AMS-bay identification is at arm's length where the swatch and
  ID are enough.

  Server-side rendering via ReportLab + qrcode (already a dep). Pure
  Python, no headless browser, no system libs. Output is byte-identical
  across browsers, Avery sheets align to <0.1 mm, and bulk export is
  one click for one PDF. Two endpoints — POST /inventory/labels (local
  DB) and POST /spoolman/labels (Spoolman-backed) — gated on
  INVENTORY_READ, capped at 500 spools per request, returning
  application/pdf via StreamingResponse. The renderer is decoupled
  from the SQLAlchemy model via a LabelData dataclass so the same code
  path serves both modes.

  Modal picker scales to large libraries: search (substring match
  across name / brand / #ID), material filter chips derived from the
  visible spools, additive Select-all-visible / Deselect-visible /
  Clear-all actions so selections survive filter changes. Restyled
  twice in development — first cut used generic Tailwind which clashed
  with the inventory's bambu-dark palette; second cut switched to
  bambu-dark-secondary / bambu-green / bambu-gray to match.

  Two render bugs found during visual inspection of generated PDFs and
  fixed before commit:

    1. AMS-30x15 template originally produced labels with only swatch
       + QR and no text at all — the side-by-side layout left <5 mm
       for the text column, so the renderer bailed without drawing
       anything. Layout split into tight (h<20mm) and roomy (h>=20mm)
       regimes; tight regime drops the QR and gives the right column
       to brand + material + a 13pt-bold spool ID.

    2. Box-62x29 template aggressively truncated text — swatch + QR
       each at ~14 mm on a 26mm-tall label squeezed the text column
       to ~16 mm, turning "Polymaker Ivory" into "Polymak..." and
       "Polymaker . PLA . Matte" into "Polymaker ...". Swatch capped
       at 16 mm, QR capped at 18 mm and constrained to ~20% of width,
       leaving the text column ~30 mm — full names render without
       truncation.

  Both bugs pinned by regression tests in test_label_renderer.py that
  render with pageCompression=0 so the resulting PDF bytes contain the
  text as ASCII and `assert b"Polymaker" in pdf` works.

frontend/src/api/client.ts

@@ -2259,6 +2259,9 @@ export interface LinkedSpoolsMap {
 }
 
 // Inventory types
+// Label printing (#809). Mirror of backend.app.services.label_renderer.TemplateName.
+export type SpoolLabelTemplate = 'ams_30x15' | 'box_62x29' | 'avery_5160' | 'avery_l7160';
+
 export interface InventorySpool {
   id: number;
   material: string;
@@ -4382,6 +4385,37 @@ export const api = {
     }),
   unassignSpool: (printerId: number, amsId: number, trayId: number) =>
     request<{ status: string }>(`/inventory/assignments/${printerId}/${amsId}/${trayId}`, { method: 'DELETE' }),
+  // ── Spool label printing (#809) ──────────────────────────────────────────
+  // Both endpoints return application/pdf. Frontend opens the resulting Blob
+  // in a new tab so the user can print or save from the browser's PDF viewer.
+  printSpoolLabels: async (data: { spool_ids: number[]; template: SpoolLabelTemplate }): Promise<Blob> => {
+    const headers: Record<string, string> = { 'Content-Type': 'application/json' };
+    if (authToken) headers['Authorization'] = `Bearer ${authToken}`;
+    const response = await fetch(`${API_BASE}/inventory/labels`, {
+      method: 'POST',
+      headers,
+      body: JSON.stringify(data),
+    });
+    if (!response.ok) {
+      const error = await response.json().catch(() => ({}));
+      throw new Error(error.detail || `HTTP ${response.status}`);
+    }
+    return response.blob();
+  },
+  printSpoolmanSpoolLabels: async (data: { spool_ids: number[]; template: SpoolLabelTemplate }): Promise<Blob> => {
+    const headers: Record<string, string> = { 'Content-Type': 'application/json' };
+    if (authToken) headers['Authorization'] = `Bearer ${authToken}`;
+    const response = await fetch(`${API_BASE}/spoolman/labels`, {
+      method: 'POST',
+      headers,
+      body: JSON.stringify(data),
+    });
+    if (!response.ok) {
+      const error = await response.json().catch(() => ({}));
+      throw new Error(error.detail || `HTTP ${response.status}`);
+    }
+    return response.blob();
+  },
   getSpoolCatalog: () =>
     request<SpoolCatalogEntry[]>('/inventory/catalog'),
   addCatalogEntry: (data: { name: string; weight: number }) =>