Add settings page for managing forecasting API key and URL via UI

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

frontend/node_modules/internal-slot/.editorconfig

@@ -0,0 +1,20 @@
+root = true
+
+[*]
+indent_style = tab
+indent_size = 4
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+max_line_length = 150
+
+[CHANGELOG.md]
+indent_style = space
+indent_size = 2
+
+[*.json]
+max_line_length = off
+
+[Makefile]
+max_line_length = off