Summary

Create new crates/zeph-common/ utility crate and consolidate the three independent truncate_to_bytes implementations.

Current duplicates

• zeph-mcp/src/sanitize.rs — returns String
• zeph-memory/src/sqlite/preferences.rs — returns &str
• zeph-memory/src/graph/resolver.rs — returns &str

Acceptance criteria

• truncate_to_bytes exists only in zeph-common::text; all 3 callers import from there
• zeph-common has no zeph-* dependencies (pure utility, no business logic)
• All existing tests pass

Part of EPIC-01 (Shared Utilities Crate)