Update CLI to be fully compliant with JSON schemas

- cache/types.rs: Update SymbolType, Stability, add Language/Visibility enums,
  restructure FileEntry and SymbolEntry, add source_files to Cache
- vars/mod.rs: Simplify VarsFile and VarEntry to match vars.schema.json
- config/mod.rs: Add schema-compliant structure with optional sections
- index/indexer.rs: Populate source_files, detect language, update generate_vars
- parse/mod.rs: Use new schema-compliant types
- main.rs: Fix references to removed fields, add output directory creation
- query.rs: Update to work with new Cache structure
- .gitignore: Add .acp/ generated output directory

Author: ddunnock

.gitignore

@@ -52,4 +52,6 @@ examples/**/.acp.vars.json
 
 # Documentation build
 docs/_build/
-site/
+site/
+# ACP generated output
+.acp/