agent: lumotia-rebrand — drop MagnotiaError prefix, now lumotia_core::Error

Phase 3 of the rebrand cascade per locked decision D4. MagnotiaError ->
Error in crates/core/src/error.rs (the crate name already qualifies it).
92 usages across 14 .rs files renamed via word-boundary sed.

One collision required disambiguation: lumotia_storage already had its
own local Error type (introduced by the slop-pass Area A residuals work).
crates/storage/src/error.rs aliases the imported core error as CoreError
on import; the From<Error> for CoreError boundary impl and the
CoreError::Storage construction site use the alias.

cargo build --workspace passes. cargo test --workspace: 330 pass, 0 fail.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/core/src/lib.rs

@@ -9,7 +9,7 @@ pub mod recommendation;
 pub mod tuning;
 pub mod types;
 
-pub use error::{MagnotiaError, Result};
+pub use error::{Error, Result};
 pub use types::{
     AudioSamples, DownloadProgress, EngineName, Megabytes, ModelId, Segment, Transcript,
     TranscriptionOptions,