[Phase 2] Add Workspace Symbols for Cross-File Navigation

[vogella]

Description

Implement workspace symbol provider to search for symbols across all AsciiDoc files in the workspace.

Goals

• Enable cross-file search (Ctrl+Shift+T or similar)
• Find headers, includes, images, anchors across all .adoc files
• Relevance-based ranking (exact match > starts with > contains)

Implementation

Add WorkspaceSymbolProvider capability to LSP server and implement symbol extraction across workspace files.

Key Features

1. Search document titles and sections
2. Find includes and images by name
3. Find anchor definitions [[anchor-name]]
4. Navigate to symbol location in any file
5. Cache results for performance

Testing

• Search finds symbols across multiple files
• Relevance ranking works
• Navigation jumps to correct file/line
• Performance acceptable for 100+ files

Dependencies

• Depends on: [Phase 1] Connect LSP Server to .adoc Content Type #27, [Phase 1] Implement Proper AsciiDoc Document Symbols #31 (reuse symbol extraction logic)

Priority: Medium