feat(transition): cross-source task deduplication

[LarsCowe]

Problem

import_tasks_from_sources() combines tasks from multiple sources (beads, GitHub, PRD files) without deduplication. If the same task exists in both GitHub Issues and a PRD file, it appears twice in the fix plan.

Proposal

Before combining sources, normalize titles and deduplicate:

1. Lowercase, strip punctuation, trim whitespace
2. Compare first 50 characters for fuzzy matching
3. Keep the most specific version (prefer GitHub issue with ID over PRD bullet)

Files

• ralph/lib/task_sources.sh — import_tasks_from_sources() (line 517)

Priority

Not in top 16 — Low impact, 2 hours effort