Tech-Debt: Implement get_dependencies endpoint

[raifdmueller]

Description

Implement get_dependencies MCP tool as specified in 02_api_specification.adoc:582-607.

API Response Format

{
  "include_tree": {
    "arc42.adoc": [
      "chapters/01_introduction.adoc",
      "chapters/02_constraints.adoc"
    ]
  },
  "cross_references": [
    {
      "from": "decisions.adr-001",
      "to": "constraints.technical",
      "type": "reference"
    }
  ]
}

Implementation Requirements

include_tree (Medium effort)

• Extend StructureIndex to store include information from parsing
• Access AsciidocDocument.includes (IncludeInfo) during indexing
• Build tree structure mapping files to their includes

cross_references (Higher effort)

• Implement xref:: and <<>> parsing in AsciiDoc parser
• Track references between sections
• Map references to section paths

Related

• Split from Issue API: Meta-Information Endpoints (metadata, validate) #10 (Meta-Information API)
• Use-Case: UC-06 (Extension)