feat(web): wire gerbview tool (file-less launch, wizard-skip, UI)

Register the newly WASM-ported Gerber Viewer in the web app the same way as
the other tools — registry entries only, no UI edits (ProjectDetailPage renders
launch links generically from FILELESS_TOOLS).

GERBVIEW_FRAME opens gerber/drill files through its own File→Open UI and projects
carry no gerber files to auto-open, so it's treated as file-less (boot standalone),
mirroring symbol_editor. It boots through single_top.cpp's STARTWIZARD, so it seeds
config to skip the first-run wizard (TOOL_NEEDS_CONFIG_SEED) and gets a
/usr/bin/gerbview argv0.

- contract: add "gerbview" to TOOLS, TOOL_LABELS ("Gerber Viewer"), FILELESS_TOOLS
- frontend: add gerbview to TOOL_ARGV0 and TOOL_NEEDS_CONFIG_SEED
- e2e: add file-less gerbview case to tools-open.spec.ts (title "Gerber Viewer",
  canvas painted, wizard-free, no WASM abort)

Verified in-browser via npm run test:web: gerbview boots wizard-free with the
viewer chrome (toolbars + layers manager), 0 console errors.

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

tests/web/tools-open.spec.ts

@@ -26,6 +26,7 @@ const CASES: Record<string, ToolCase> = {
   pl_editor: { route: 'pl_editor/demo.kicad_wks', titleRe: /demo — Drawing Sheet Editor/i, fileless: false },
   calculator: { route: 'calculator/', titleRe: /Calculator Tools/i, fileless: true },
   symbol_editor: { route: 'symbol_editor/', titleRe: /Symbol Editor/i, fileless: true },
+  gerbview: { route: 'gerbview/', titleRe: /Gerber Viewer/i, fileless: true },
 };
 
 /** Console text that must never appear (wizard-crash + URL-regex modal markers). */