feat: expose file outline and symbol lookup as MCP tools

[jordanpartridge]

SymbolIndexService has getFileOutline() and getSymbol() methods that allow structural code navigation — browsing symbols in a file and looking up symbol metadata by ID.

These should be exposed as MCP tools so Claude can navigate codebases structurally, not just semantically.

Suggested tools:

• FileOutlineTool — given a file path + repo, return the symbol hierarchy
• SymbolLookupTool — given a symbol ID + repo, return metadata and source

Files:

• app/Services/SymbolIndexService.php (existing methods)
• app/Mcp/Servers/KnowledgeServer.php (register new tools)