agent: lumotia-rebrand — data dir migration shim + paths.rs rename

Phase 5 of the rebrand cascade per locked decision D1 (migrate in place).

crates/core/src/paths.rs:
- Hardcoded subdir strings renamed: magnotia/Magnotia -> lumotia/Lumotia
  across all four OS branches (Linux XDG + dot-legacy, macOS Application
  Support, Windows LOCALAPPDATA, fallback dot-dir).
- Database filename: magnotia.db -> lumotia.db.
- Test path fixtures renamed: /tmp/magnotia-test -> /tmp/lumotia-test.
- New MigrationStatus enum (Migrated / TargetAlreadyExists / NoLegacyFound).
- New migrate_legacy_data_dir() that probes the platform-correct legacy
  magnotia path, renames it to the lumotia equivalent via fs::rename, and
  also renames magnotia.db -> lumotia.db inside if found. Idempotent: safe
  to call on every boot. Refuses to overwrite an existing lumotia dir to
  protect user data.
- Four new unit tests covering all branches via the test-friendly
  migrate_legacy_data_dir_inner that takes an explicit legacy path.

crates/storage/src/database.rs:
- New migrate_legacy_setting_keys(pool) that renames any settings rows
  with key matching magnotia_* to lumotia_*. Single SQL UPDATE with
  NOT EXISTS guard so it leaves rows alone if a lumotia_ row already
  exists. Re-exported from lib.rs.

src-tauri/src/lib.rs:
- Calls migrate_legacy_data_dir(&app_data_dir()) at the start of setup()
  BEFORE database_path() resolves the now-renamed dir. Logs migration
  outcome to lumotia_startup tracing target.
- Calls migrate_legacy_setting_keys(&db) immediately after init_db
  returns. Logs only when rows are actually renamed.

src-tauri/src/{lib,commands/{diagnostics,rituals,transcripts}}.rs +
crates/storage/src/database.rs:
- All in-code references to magnotia_preferences, magnotia_history (in
  comments), and magnotia_morning_triage_last_shown renamed to lumotia_*.

cargo build --workspace passes. cargo test --workspace: 334 pass, 0 fail
(up from 330; +4 paths::tests).

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

crates/storage/src/database.rs

@@ -905,6 +905,31 @@ pub async fn get_setting(pool: &SqlitePool, key: &str) -> Result<Option<String>>
     Ok(row.map(|r| r.get("value")))
 }
 
+/// One-shot key rename for settings rows carried over from the magnotia era
+/// (`magnotia_preferences`, `magnotia_morning_triage_last_shown`, etc.).
+///
+/// Idempotent: rows already on the new key are left alone; rows on the old
+/// key are renamed only if the new key does not already exist. Returns the
+/// number of rows actually renamed so the caller can log on first launch.
+pub async fn migrate_legacy_setting_keys(pool: &SqlitePool) -> Result<u64> {
+    let result = sqlx::query(
+        "UPDATE settings \
+         SET key = 'lumotia_' || substr(key, length('magnotia_') + 1) \
+         WHERE key LIKE 'magnotia_%' \
+           AND NOT EXISTS (\
+               SELECT 1 FROM settings AS dst \
+               WHERE dst.key = 'lumotia_' || substr(settings.key, length('magnotia_') + 1)\
+           )",
+    )
+    .execute(pool)
+    .await
+    .map_err(|source| Error::Query {
+        operation: "migrate_legacy_setting_keys".into(),
+        source,
+    })?;
+    Ok(result.rows_affected())
+}
+
 // --- Row types ---
 
 #[derive(Debug, Clone)]
@@ -944,7 +969,7 @@ pub struct TranscriptRow {
     pub anti_hallucination: bool,
     pub created_at: String,
     // Task 2.5 — transcripts_meta (migration v5). Persists the UI metadata
-    // that previously lived in the removed localStorage `magnotia_history` cache.
+    // that previously lived in the removed localStorage `lumotia_history` cache.
     pub starred: bool,
     pub manual_tags: String,
     pub template: String,