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/model_manager.rs

@@ -2,7 +2,7 @@ use std::collections::HashSet;
 use std::path::{Path, PathBuf};
 use std::sync::{LazyLock, Mutex};
 
-use lumotia_core::error::{MagnotiaError, Result};
+use lumotia_core::error::{Error, Result};
 use lumotia_core::model_registry::{find_model, ModelFile};
 use lumotia_core::types::{DownloadProgress, ModelId};
 
@@ -18,9 +18,9 @@ impl DownloadReservation {
         let id = id.as_str().to_string();
         let mut active = ACTIVE_DOWNLOADS
             .lock()
-            .map_err(|_| MagnotiaError::DownloadFailed("download lock poisoned".into()))?;
+            .map_err(|_| Error::DownloadFailed("download lock poisoned".into()))?;
         if !active.insert(id.clone()) {
-            return Err(MagnotiaError::DownloadFailed(format!(
+            return Err(Error::DownloadFailed(format!(
                 "download already in progress for {id}"
             )));
         }
@@ -80,7 +80,7 @@ pub async fn download(
     progress: impl Fn(DownloadProgress) + Send + 'static,
 ) -> Result<()> {
     let _reservation = DownloadReservation::acquire(id)?;
-    let entry = find_model(id).ok_or_else(|| MagnotiaError::ModelNotFound(id.clone()))?;
+    let entry = find_model(id).ok_or_else(|| Error::ModelNotFound(id.clone()))?;
 
     let dir = model_dir(id);
     std::fs::create_dir_all(&dir)?;
@@ -98,7 +98,7 @@ pub async fn download(
                     let _ = std::fs::remove_file(&dest);
                 }
                 Err(e) => {
-                    return Err(MagnotiaError::DownloadFailed(format!(
+                    return Err(Error::DownloadFailed(format!(
                         "failed to verify existing {}: {e}",
                         file.filename
                     )));
@@ -196,7 +196,7 @@ async fn download_file(
     let client = reqwest::Client::builder()
         .connect_timeout(std::time::Duration::from_secs(30))
         .build()
-        .map_err(|e| MagnotiaError::DownloadFailed(e.to_string()))?;
+        .map_err(|e| Error::DownloadFailed(e.to_string()))?;
 
     // Check for existing partial download (resume support)
     let existing_bytes = if part_path.exists() {
@@ -215,7 +215,7 @@ async fn download_file(
     let response = request
         .send()
         .await
-        .map_err(|e| MagnotiaError::DownloadFailed(e.to_string()))?;
+        .map_err(|e| Error::DownloadFailed(e.to_string()))?;
 
     // If we requested Range but the server returned 200 (full file), the
     // server does not support resume. Rather than blindly appending a
@@ -237,14 +237,14 @@ async fn download_file(
                 false
             }
             other => {
-                return Err(MagnotiaError::DownloadFailed(format!(
+                return Err(Error::DownloadFailed(format!(
                     "resume request returned unexpected status {other}"
                 )));
             }
         }
     } else {
         if !response.status().is_success() {
-            return Err(MagnotiaError::DownloadFailed(format!(
+            return Err(Error::DownloadFailed(format!(
                 "download returned HTTP {} for {}",
                 response.status(),
                 file.filename
@@ -291,7 +291,7 @@ async fn download_file(
     }
 
     while let Some(chunk) = stream.next().await {
-        let chunk = chunk.map_err(|e| MagnotiaError::DownloadFailed(e.to_string()))?;
+        let chunk = chunk.map_err(|e| Error::DownloadFailed(e.to_string()))?;
         std::io::Write::write_all(&mut out, &chunk)?;
         hasher.update(&chunk);
         downloaded += chunk.len() as u64;
@@ -319,7 +319,7 @@ async fn download_file(
     let actual = format!("{:x}", hasher.finalize());
     if actual != file.sha256 {
         let _ = std::fs::remove_file(&part_path);
-        return Err(MagnotiaError::DownloadFailed(format!(
+        return Err(Error::DownloadFailed(format!(
             "SHA256 mismatch for {}: expected {}, got {}",
             file.filename, file.sha256, actual
         )));