refactor: replace aeson ToJSON/FromJSON with json-fleece schemas

- RecipeSearchEntry: replace genericToJSON ToJSON with Fleece schema
  using object combinators (required, optionalNullable, list text)
- SchemaOrgRecipe: replace manual FromJSON instance with Fleece decoder
  that reuses existing helper functions for quirky fields
- Html.hs: use Fleece.Aeson.Encoder.encode instead of Data.Aeson.encode
- stack.yaml: add shrubbery + json-fleece extra-deps
- package.yaml: add json-fleece-aeson + json-fleece-core deps
- Remove unused LANGUAGE pragmas and redundant brackets

stack.yaml

@@ -2,3 +2,14 @@ resolver: lts-24.38
 
 packages:
   - .
+
+extra-deps:
+  - github: flipstone/shrubbery
+    commit: 1847db5c280357ff341b5909250981b8c303f444
+    subdirs:
+      - .
+  - github: flipstone/json-fleece
+    commit: f2df040dee441a25dd1bbdc8bcf939bf04c74875
+    subdirs:
+      - json-fleece-core
+      - json-fleece-aeson