Add comprehensive test suite and fix error handling in MCP server
Tests (70 tests, all passing):
- TestEncode: 12 tests — text, file, encryption, channels, strategies,
bit depth, compression, default paths, error cases
- TestDecode: 12 tests — auto-detect, manual config, encryption,
wrong password, binary payloads, strategy-specific behavior
- TestAnalyze: 5 tests — clean/stegged images, full mode, channel fields
- TestCapacity: 4 tests — default, single channel, high bits, errors
- TestDetect: 3 tests — clean, stegged, missing image
- TestChunks: 7 tests — tEXt/zTXt/iTXt/private chunk inject+read
- TestInjectExif: 6 tests — fields, custom JSON, validation
- TestInjectionFilename: 4 tests — templates, count, channels
- TestJailbreakTemplates: 2 tests — listing and preview truncation
- TestAnalysisTools: 7 tests — rs_analysis, chi_square, unicode steg,
unknown action, missing file
- TestCryptoStatus: 2 tests — availability and method listing
- TestIntegration: 6 tests — full pipeline, encrypted pipeline,
chunk+steg coexistence, large payload, sequential strategy, EXIF
MCP server fixes:
- All tools now return JSON errors instead of raising exceptions
- Custom JSON encoder handles numpy bool_/integer/floating/ndarray
- Discovered upstream bug: spread and randomized strategies fail to
decode (steg_core.py issue, not MCP server)
7ef3ec5368