Fix critical documentation errors

[PJK]

Summary

• Fix swapped Doxygen comments in callbacks.h: definite/indefinite labels were reversed for byte strings, arrays, and maps. Since streaming_decoding.rst auto-generates from these via doxygenstruct, the streaming API docs showed wrong descriptions.
• Fix CBOR encoding example in byte strings docs: 0xf5 (boolean true) -> 0x5f (indefinite byte string start)
• Fix CBOR encoding example in arrays docs: 0x9f (indefinite array) described as definite -> 0x98 (definite array, 1B length)
• Fix missing item argument in cbor_set_uint8 code example (wouldn't compile)
• Fix "positive integer" -> "negative integer" in Type 1 section (copy-paste error)
• Fix CMake minimum version: 2.8 -> 3.5 (actual requirement since PR Set cmake_minimum_required to 3.5 #355)
• Fix swapped cross-references in streaming encoding docs (strings linked to byte strings page and vice versa)

Test plan

• All 26 tests pass
• Visual review of all changes

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (55408c6) to head (4e3d565).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #398   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           20        20           
  Lines         1663      1663           
=========================================
  Hits          1663      1663           

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