Task 17.9: Pure Python decoder validated at 67-74% accuracy

Validated against Unicorn on all 7 FBL files:
  Vatican: 74%, Monaco: 71%, SanMarino: 74%
  Gibraltar: 68%, Andorra: 71%, Liechtenstein: 69%, Malta: 67%

The remaining 26-33% gap includes:
- Graph builder records (0x80320000 etc.) not generated by decoder
- # hash NUL delimiter scan alignment
- Junction records from group mode

The decoder correctly handles: varints, whitespace, # hash to NUL,
\ escapes (table + \Q/\E), metacharacters (^ $ | * + . ? [ { ( ) ] }),
NUL as data, and { as data unless valid {n,m}.

Author: mretallack

.kiro/specs/map-decryption/tasks.md

@@ -870,7 +870,7 @@ would be more portable.
 - [x] **17.6** Translate pattern quantifiers (* + ? {n,m})
 - [x] **17.7** Translate character class [ ] handling
 - [x] **17.8** Translate ^ $ | metacharacter → control record mapping
-- [ ] **17.9** Validate against Unicorn output on all 7 test files
+- [x] **17.9** Validate against Unicorn output on all 7 test files
 - [ ] **17.10** Remove Unicorn dependency from nng_decoder.py
 
 ## 18. Head Unit Testing