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/transcription/src/whisper_rs_backend.rs

@@ -10,7 +10,7 @@ use std::path::Path;
 
 use whisper_rs::{FullParams, SamplingStrategy, WhisperContext, WhisperContextParameters};
 
-use lumotia_core::error::{MagnotiaError, Result};
+use lumotia_core::error::{Error, Result};
 use lumotia_core::hardware::vulkan_loader_available;
 use lumotia_core::tuning::{inference_thread_count, Workload};
 use lumotia_core::types::{Segment, TranscriptionOptions};
@@ -65,7 +65,7 @@ impl Transcriber for WhisperRsBackend {
         );
 
         let mut state = self.ctx.create_state().map_err(|e| {
-            MagnotiaError::TranscriptionFailed(
+            Error::TranscriptionFailed(
                 WhisperBackendError::State(e.to_string()).to_string(),
             )
         })?;
@@ -88,7 +88,7 @@ impl Transcriber for WhisperRsBackend {
         params.set_print_realtime(false);
 
         state.full(params, samples).map_err(|e| {
-            MagnotiaError::TranscriptionFailed(
+            Error::TranscriptionFailed(
                 WhisperBackendError::Transcribe(e.to_string()).to_string(),
             )
         })?;
@@ -103,7 +103,7 @@ impl Transcriber for WhisperRsBackend {
             let text = seg
                 .to_str()
                 .map_err(|e| {
-                    MagnotiaError::TranscriptionFailed(
+                    Error::TranscriptionFailed(
                         WhisperBackendError::Transcribe(e.to_string()).to_string(),
                     )
                 })?