feat(two-bucket): add BFS and Extended GCD approaches for W39 48in24

[haaeppyy]

tag: #221
What this PR does:
Adds .approaches folder for the two-bucket exercise to enable the "Dig Deeper" feature for W39 #48in24, as requested in the issue.
Approaches added:

1. Breadth-First Search — state-space search (matches example solution)
2. Extended GCD — mathematical approach using Extended Euclidean Algorithm
   Files:

• .approaches/config.json — metadata with UUIDs, slugs, blurbs
• .approaches/introduction.md — overview with trade-offs
• .approaches/bfs/content.md + snippet.txt (8 lines)
• .approaches/egcd/content.md + snippet.txt (8 lines)
  Notes:
• First exercise in V track with approaches — follows Exercism standard format (referenced Go track examples)
• Snippets ≤8 lines per Exercism requirements
• Ready for W39 feature
• Add .approaches/config.json with metadata for both approaches
• Add .approaches/introduction.md with overview and trade-offs
• Add .approaches/bfs/content.md with detailed BFS explanation
• Add .approaches/bfs/snippet.txt with core BFS logic (8 lines)
• Add .approaches/egcd/content.md with Extended GCD mathematical approach
• Add .approaches/egcd/snippet.txt with egcd implementation (8 lines)

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[keiravillekode]

Have you solved this exercise in Exercism using these two approaches, and published the solutions?

i.e. do they appear in Community Solutions?

I think it would be helpful if each approach content.md started with a full working code example. As far as I can tell, that is what every Go approach does.

[keiravillekode]

Please run

bin/fetch-configlet
bin/configlet lint