feat(analysis): add DependaChartaImporter for code-level dependency edges

Import .dc.json files produced by DependaCharta and convert class/function-level
dependencies into aggregated file-level edges in cc.json format. Includes full
ccsh integration, interactive dialog, documentation, and 87% test coverage.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>