feat: "references" repos in local projects

[bmdavis419]

Greptile Summary

Added btca reference command to clone git repositories into ./references/<repo-name> for use as read-only reference context. Also refactored SSE stream parsing to properly handle edge cases where data chunks are split across network boundaries.

Key changes:

• New reference command clones repos and adds them to .git/info/exclude automatically
• Improved SSE parser handles split chunks and delayed blank-line terminators
• Error handling in ask command now throws proper BtcaError instead of just logging
• Comprehensive test coverage added for all new functionality
• Documentation updated in both README and docs site

Confidence Score: 5/5

• Safe to merge - well-tested feature addition with no breaking changes
• New feature is self-contained, existing commands unchanged, comprehensive tests added, follows project style guide, and documentation is complete
• No files require special attention

Important Files Changed

Filename	Overview
apps/cli/src/commands/reference.ts	New command to clone reference repos into ./references/ with git exclude support
apps/cli/src/client/stream.ts	Refactored SSE parser to handle split chunks and edge cases correctly
apps/cli/src/commands/ask.ts	Extracted error handling to streamErrorToBtcaError helper, throws instead of logging

_{Last reviewed commit: 582b44a}

[bmdavis419]

• feat: "references" repos in local projects #187 👈 (View in Graphite)
• main

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