03: new article — exe_crunchers.md (executable packers deep dive)

New comprehensive article on Amiga executable crunchers covering:
- Architecture: how crunched files remain valid HUNK executables
- Major crunchers: PowerPacker, Imploder, Shrinkler, ByteKiller,
  Titanics, CrunchMania, PackFire, XPK framework
- PP20 format: efficiency table, decrunch info, decrunch colours
- Shrinkler internals: 1536-context adaptive probability model,
  range coder, parity context flag, stack-based context table,
  actual 68000 decompressor source from GitHub
- LZ77/LZSS vs context-modelling+range-coding algorithms
- Relocation handling: 3 strategies (compressed relocs, delta
  table, merged single-hunk)
- Memory layout diagrams: before/during/after decompression
- Detection: magic signatures table, fake header warning,
  Python scanner script
- Tools: xfdmaster modular architecture, Ancient C++ library,
  debugger-based extraction (last resort)
- FPGA/emulation impact: timing, self-modifying code, cache

Based on web research: verified PP20 format spec, Shrinkler
source (askeksa/Shrinkler), Ancient library (temisu/ancient),
xfdmaster slave module architecture.

Updated indexes: 03/README.md, root README.md

README.md

@@ -98,6 +98,7 @@ The Amiga's documentation was scattered across out-of-print manuals, Usenet post
 | [exe_load_pipeline.md](03_loader_and_exec_format/exe_load_pipeline.md) | LoadSeg → AllocMem → relocation → segment chain → CreateProc → entry point |
 | [object_file_format.md](03_loader_and_exec_format/object_file_format.md) | HUNK_UNIT object files, multi-section layout, HUNK_LIB archives, linker operation |
 | [overlay_system.md](03_loader_and_exec_format/overlay_system.md) | HUNK_OVERLAY: tree architecture, runtime overlay manager, modern alternatives |
+| [**exe_crunchers.md**](03_loader_and_exec_format/exe_crunchers.md) | **Executable packers: PP20/Imploder/Shrinkler, decrunch stubs, algorithms, detection** |
 
 ### 04 — Linking & Library Integration
 | File | Topic |