feat(compression): add reversible Huffman coding

[google-labs-jules]

Summary

• add lossless Huffman Coding (1951) compression and decompression
• use a deterministic self-contained binary format instead of Java object serialization
• handle single-symbol inputs, arbitrary byte values, malformed/truncated payloads, and empty input
• integrate Huffman into the current editor without losing RLE or LZW
• generate both Compress and Decompress UI actions from one shared helper so compression algorithms are always exposed symmetrically
• add JUnit round-trip coverage for Huffman, RLE, and LZW
• add repository CI for the Java build/test suite
• document the algorithm and reversible format

Reversibility invariant

Every compression algorithm exposed by Eddy must provide and validate both directions:

decompress(compress(input)) == input

The same principle applies to encryption algorithms: every encrypt operation must have its matching decrypt operation.

Validation

• Huffman round-trip validated for empty input, repeated single-symbol data, UTF-8 text, all 256 byte values, and random binary payloads
• malformed Huffman payload rejection covered
• repository test suite included via Gradle/JUnit

Closes #1

[google-labs-jules]

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