zig: add 0.15 gzip bug, tangled packages, codeberg issue tracking
- io.md: document flate.Decompress panic on x86_64-linux, workaround
- dependencies.md: tangled.sh as zig package source
- 0.15/README.md: zig issues moved to codeberg (30xxx+)
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>