Eliminate Python dependency: embed frontend assets in odoo-go

- Copy all OWL frontend assets (JS/CSS/XML/fonts/images) into frontend/
  directory (2925 files, 43MB) — no more runtime reads from Python Odoo
- Replace OdooAddonsPath config with FrontendDir pointing to local frontend/
- Rewire bundle.go, static.go, templates.go, webclient.go to read from
  frontend/ instead of external Python Odoo addons directory
- Auto-detect frontend/ and build/ dirs relative to binary in main.go
- Delete obsolete Python helper scripts (tools/*.py)

The Go server is now fully self-contained: single binary + frontend/ folder.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/sale/static/src/js/quantity_buttons/quantity_buttons.scss

@@ -0,0 +1,22 @@
+input[name="sale_quantity"] {
+    padding: 0;
+
+    @include media-breakpoint-down(md) {
+        max-width: 3rem;
+    }
+
+    @include media-breakpoint-up(md) {
+        max-width: 4rem;
+    }
+    
+    // removing input field=number arrows as their size might
+    // change depending on browser default styling and shift input's position
+    &::-webkit-outer-spin-button,
+    &::-webkit-inner-spin-button {
+        -webkit-appearance: none;
+        margin: 0;
+    }
+    &[type=number] {
+        -moz-appearance: textfield;
+    }
+}