perf(invoices): lazy-load pdf-lib + swissqrbill, -516 KB on route

/(app)/invoices/[id] route bundle drops from **534 KB → 18.6 KB** by
moving PDF rendering behind dynamic imports.

Changes:
  - views/DetailView.svelte: `await import('../pdf/renderer')` inside
    renderPdf() + downloadPdf(), cached in a module-local ref.
  - components/SendModal.svelte: same for openAndDownload().
  - pdf/scor.ts (new): generateSCORReference extracted so the
    invoices store can derive a reference string without pulling
    swissqrbill/svg + pdf-lib into the list-view bundle.
  - pdf/qr-bill.ts: re-exports generateSCORReference from scor.ts
    for backward compatibility.
  - stores/invoices.svelte.ts: imports from ../pdf/scor (light) instead
    of ../pdf/qr-bill (heavy).
  - index.ts: drop re-export of the PDF renderer from the module
    barrel so `import ... from '$lib/modules/invoices'` never drags
    pdf-lib in.

The heavy chunk (pdf-lib + swissqrbill, ~576 KB) now only loads when
a user actually opens an invoice detail — list views, create flow, and
all other routes stay lean.

20/20 qr-bill tests pass; svelte-check clean.

Bonus: scripts/audit-icon-usage.mjs (+ pnpm run audit:icon-usage)
audits @mana/shared-icons imports. Reveals 204 distinct icons across
the codebase, 199 of them at default weight but paying for all 6
Phosphor weights. Biggest offender: app-registry/apps.ts with 69
static icon imports accounting for ~290 KB of the shared 466 KB icon
chunk. Migration path for that is documented in
docs/optimizable/bundle-analysis.md §2 — next session's work.

docs/optimizable/bundle-analysis.md also updated with the root (app)
layout (260 KB) investigation notes (start/stop lifecycle hooks to
defer via idleCallback).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -36,6 +36,7 @@
 		"audit:port-drift": "node scripts/audit-port-drift.mjs",
 		"audit:test-coverage": "node scripts/audit-test-coverage.mjs",
 		"audit:bundle": "node scripts/audit-bundle.mjs",
+		"audit:icon-usage": "node scripts/audit-icon-usage.mjs",
 		"audit:all": "pnpm run audit:port-drift && pnpm run audit:i18n-coverage --summary && pnpm run audit:test-coverage --summary",
 		"generate:dockerfiles": "node scripts/generate-dockerfiles.mjs",
 		"setup:env": "node scripts/generate-env.mjs",