v0.80.0-alpha.1 — nika-error admitted

The first tag of the Diamond rebuild (orphan branch created 2026-04-13 — zero shared history with the exploration era). nika-error (L0) admitted through all 12 gates: typed NIKA-XXX error hierarchy, miette integration for diagnostics, per-crate error range allocation, proptest-backed roundtrip invariants.

📚 Historical foundation tag — no binaries (the release pipeline starts at v0.90.0). The full arc.