feat: add annotation type support to parser and autocomplete

[abanchev]

Summary

• Parse @interface declarations in ASTFactory — previously the parser threw an IOException when encountering annotation type declarations, preventing the entire source file from being parsed
• Filter completions after @ to show only annotation types, not methods/fields/local variables
• Add annotation parameter completion inside @Annotation(...) with element names and Javadoc from source attachments
• Add isAnnotationType() helper to ClassCompletion using ACC_ANNOTATION access flag

Motivation

The parser had no support for @interface declarations at all. When a source file contained an annotation type definition (e.g. @interface Serialize), the ASTFactory threw an IOException which was caught and treated as a parse error — meaning the entire file couldn't be parsed and no completions were available.

Additionally, typing @ before an annotation name showed all completions (methods, fields, local variables) instead of filtering to just annotation types. And inside annotation parentheses like @Serialize(tooltip=..., readOnly=...), there was no completion for the annotation's element names.

Changes

Parser (ASTFactory.java):

• getClassOrInterfaceDeclaration: ANNOTATION_START case consumes @ + interface keyword, delegates to getNormalInterfaceDeclaration
• getInterfaceMemberDecl: tolerates default clauses on annotation elements

Autocomplete (SourceCompletionProvider.java):

• isAnnotationContext(): detects @ character before entered text
• Annotation type filtering: when in @ context, removes non-annotation completions
• getAnnotationClassName(): scans backward through balanced parens to detect @Name(...) context
• addAnnotationElementCompletions(): resolves annotation ClassFile, iterates element methods, creates completions with Javadoc from source

ClassCompletion.java:

• isAnnotationType(): checks ACC_ANNOTATION bit on class access flags

Test plan

• 4 new AnnotationTypeDeclarationTest cases: simple @interface, with defaults, with imports, body elements
• 2 new SourceCompletionProviderTest cases: @ prefix detection
• All existing tests pass
• Manual testing: @Ser shows only annotation types, @Serialize( shows element names with Javadoc