feat(collections): add per-collection slugify option for path indexing

[klokie]

Summary

• Adds a slugify option to the Collection interface (default: true for backward compatibility)
• When slugify: false, filenames are stored as-is during indexing, preserving spaces, uppercase, and special characters
• Fixes path resolution for files like BASS PLAYER Lesson 02.md which were previously slugified to bass-player-lesson-02.md

Motivation

QMD normalizes filenames to kebab-case during indexing via handelize(). This breaks path resolution for downstream tools (e.g. qmd-search-obsidian) when files have spaces or uppercase characters in their names. Making it configurable preserves backward compatibility while letting users opt in to original-path preservation.

Usage

# ~/.config/qmd/index.yml
collections:
  notes:
    path: /Users/me/Documents/notes
    pattern: "**/*.md"
    slugify: false   # preserve original filenames

Test plan

• New test: default behavior (slugify: true) still handleizes paths to kebab-case
• New test: slugify: false preserves original filenames with spaces and uppercase
• New test: search results return original filenames when slugify: false
• All existing tests pass (450 tests across 7 test files)
• Manual test: index a collection with slugify: false containing files with spaces, verify qmd search --json returns correct paths

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