Use working directory as project root instead of marker-based detection

[gregology]

Summary

Fixes #44. findProjectRoot was walking up from the target file looking for markers like .git, pyproject.toml, Makefile, etc. In monorepos where a subdirectory has its own pyproject.toml, it'd stop there and never reach the actual root. So the root AGENTS.yaml just vanished.

The fix: stop guessing. Use the working directory instead of marker detection.

• Hook mode (sctx hook): uses the cwd field from Claude Code's JSON input, which is the directory where claude was launched
• CLI mode (sctx context, sctx decisions): uses os.Getwd(), so wherever you run sctx from is the root

findProjectRoot is deleted entirely. No fallback to markers. The root is always explicit and predictable.

Changes:

• Added Root field to ResolveRequest
• Resolve() uses req.Root when set, falls back to os.Getwd()
• Claude adapter passes hookInput.CWD as Root
• Removed findProjectRoot() and all .git marker files from tests
• Updated protocol.md, README, and cli-reference docs