Add YAML platform registry (#11)

[C0MPL3XDEV]

Summary

• Replace 71 hardcoded URLs in userrecon.py with data-driven YAML registry
• New eagleosint/platforms.yaml with name, url_template, category per platform
• New eagleosint/registry.py with load, filter by category, caching
• Added pyyaml>=6.0 dependency

Files changed

• eagleosint/platforms.yaml — 71 platform definitions
• eagleosint/registry.py — registry loader with caching
• eagleosint/providers/userrecon.py — uses registry instead of hardcoded list
• pyproject.toml — added pyyaml dependency
• tests/test_registry.py — 12 tests

Test plan

• All 159 tests pass
• Platform count unchanged (71)
• Category filtering works
• Custom YAML path supported