test: improve coverage for storage and handlers (Phase 6)

[fank]

Summary

• Add error path and edge case tests for storage engines and HTTP handlers
• Improves test coverage across json.go, flatbuffers.go, and handler.go

Changes

internal/storage/json_test.go (+93 lines)

Test	Purpose
TestJSONEngineInvalidGzip	Invalid gzip data error path
TestJSONEngineInvalidJSONInGzip	Invalid JSON inside gzip file
TestJSONEngineInvalidJSON	Invalid plain JSON file
TestJSONEngineEntityWithNoType	Non-map entity in entities array
TestJSONEngineEntitiesNotArray	Entities field not an array

internal/storage/flatbuffers_test.go (+186 lines)

Test	Purpose
TestFlatBuffersEngineChunkCountError	ChunkCount when manifest read fails
TestFlatBuffersEngineConvertInvalidJSON	Convert with invalid JSON input
TestFlatBuffersEngineConvertContextCancelled	Context cancellation during convert
TestFlatBuffersEngineConvertWithEvents	Conversion including events
TestFlatBuffersEngineConvertWithCrewInVehicle	Conversion with vehicle crew data

internal/server/handler_test.go (+190 lines)

Test	Purpose
TestGetOperationManifest_JSONError	Manifest load error for JSON format
TestGetOperationManifest_ProtobufReadError	Reader error for protobuf format
TestGetOperationChunk_JSONNotSupported	Chunk request on JSON format
TestGetCapture_MissingFile	Missing capture file error
TestGetCaptureFile_MissingFile	Missing file download error

Coverage Improvements

Package	Before	After
storage	92.9%	95.0%
server	89.9%	90.3%
Overall	45.6%	46.3%

Test plan

• All existing tests pass
• New tests pass
• Coverage metrics verified

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/OCAP2/web/internal/server	90.31% (+0.44%)	👍
github.com/OCAP2/web/internal/storage	95.03% (+2.13%)	👍

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Coverage by file

Changed unit test files

• github.com/OCAP2/web/internal/server/handler_test.go
• github.com/OCAP2/web/internal/storage/flatbuffers_test.go
• github.com/OCAP2/web/internal/storage/json_test.go