Add TestScenarioRoundTrip_RealFiles covering 7 real scenario files
(cat=0/1/3, T101/T103, with and without chunk1). Tests skip gracefully
when game data is absent so CI stays green.
Decoded metadata structure from analysis of 145k+ real scenario files:
- Chunk0 m[0]/m[1] = CategoryID/MainID; m[5] = str0_len (offset to
str1); m[6] = MainID (cat=0) or 0xFFFF; m[8] = constant 5.
- Chunk1 m[9]=cumOff[2], m[10]=cumOff[1], m[14]=cumOff[3],
m[15]=total_string_bytes; m[11-13]/m[16-17] = dialog script offsets
beyond the 0xFF sentinel; m[20] = constant 5; m[21] ≈ data_size.
Update docs/scenario-format.md with full field tables for both chunks.
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