feat(stacktrace): smart stack trace mapping for 4 languages

[lexasub]

Description

Add stack trace analysis feature for Python, C++, Java, and Rust with AST mapping and LLM-powered root cause analysis.

This PR introduces:

• StackTraceService — service for parsing and analyzing stack traces from 4 languages
• AST mapping — maps stack trace frames to code entities with context snippets
• Root cause analysis — LLM-based analysis with suggested fixes
• Similar issues detection — finds similar patterns in the codebase
• CLI command — ast-rag analyze-stacktrace for manual analysis
• MCP tool — analyze_stacktrace for agent workflows

Related Issue

Fixes #(issue number)

Type of Change

• New feature (non-breaking change that adds functionality)

Checklist

• My code follows the code style of this project
• I have added tests that prove my fix/feature works
• All new and existing tests passed (pytest tests/ -v)
• I have updated the documentation accordingly
• My changes generate no new warnings

Testing

# Unit tests
pytest tests/test_stack_trace.py -v

# CLI test — analyze from file
ast-rag analyze-stacktrace error.log

# CLI test — analyze from stdin
python test.py 2>&1 | ast-rag analyze-stacktrace

# CLI test — JSON output
ast-rag analyze-stacktrace error.log -o json

# CLI test — skip AST mapping (faster)
ast-rag analyze-stacktrace error.log --no-ast-mapping

# MCP integration (via MCP client)
# Tool: analyze_stacktrace