Complete end-to-end compiler review remediation

[itsfuad]

Summary

• preserve unique semantic evidence during default expansion
• make LSP diagnostic publication snapshot-safe during edits
• centralize CLI commands and project source discovery
• make dependency metadata persistence error-atomic
• unify intrinsic definitions and enforce pipeline terminal invariants

Validation

• full Go tests and vet
• LSP race tests
• bundled compiler and default-interface runtime fixture
• CLI, dependency, parser, pipeline, and LLVM focused tests

Tracking

Builds on the compiler contract-spine refactor. Remaining user-facing string construction and C bridge work stays in #29.

Stacked on the preceding contract-spine PR.