fix: add install docs and images ignored by .gitignore

Fixed .gitignore to use /install/ and /build/ with leading slash
so only the root-level colcon dirs are ignored, not
doc/lwc-doc/docs/sunrise/install/.

Adds install pages (Windows, Linux emulator, Linux workbench)
and 22 step-by-step screenshots that were never deployed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -1,6 +1,6 @@
 log/
-install/
-build/
+/install/
+/build/
 .vscode
 .idea
 venv