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/web/static/lib/bootstrap/scss/mixins/_visually-hidden.scss

@@ -0,0 +1,33 @@
+// stylelint-disable declaration-no-important
+
+// Hide content visually while keeping it accessible to assistive technologies
+//
+// See: https://www.a11yproject.com/posts/2013-01-11-how-to-hide-content/
+// See: https://kittygiraudel.com/2016/10/13/css-hide-and-seek/
+
+@mixin visually-hidden() {
+  width: 1px !important;
+  height: 1px !important;
+  padding: 0 !important;
+  margin: -1px !important; // Fix for https://github.com/twbs/bootstrap/issues/25686
+  overflow: hidden !important;
+  clip: rect(0, 0, 0, 0) !important;
+  white-space: nowrap !important;
+  border: 0 !important;
+
+  // Fix for positioned table caption that could become anonymous cells
+  &:not(caption) {
+    position: absolute !important;
+  }
+}
+
+// Use to only display content when it's focused, or one of its child elements is focused
+// (i.e. when focus is within the element/container that the class was applied to)
+//
+// Useful for "Skip to main content" links; see https://www.w3.org/TR/2013/NOTE-WCAG20-TECHS-20130905/G1
+
+@mixin visually-hidden-focusable() {
+  &:not(:focus):not(:focus-within) {
+    @include visually-hidden();
+  }
+}