Route MCP reader tools from initialize roots

[ScriptedAlchemy]

Summary

• record MCP initialize roots as connection-local route state
• resolve those roots through the client project registry
• use the resolved root as an implicit project_path only for registered read-only reader tools when the call has no explicit selector
• share the existing serve root URI decoder so startup and connection routing parse roots consistently

Verification

• RED: CARGO_TARGET_DIR=target cargo test --features test-transport --test mcp_suite initialize_roots_route_registered_reader_tools_without_explicit_selector -- --nocapture failed with tracedecay_files returning src/active.rs
• GREEN: CARGO_TARGET_DIR=target cargo test --features test-transport --test mcp_suite initialize_roots_route_registered_reader_tools_without_explicit_selector -- --nocapture
• cargo fmt --check
• CARGO_TARGET_DIR=target cargo test --features test-transport --test mcp_suite mcp_server_test:: -- --test-threads=1 currently has 2 baseline failures: test_error_tracking and test_tools_call_plain_text_failure_sets_is_error; both reproduce unchanged on /home/zack/projects/tracedecay

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