feat(watcher): inbox zero — archived raw/ originals are removed, not copied

After a note is archived into raw/processed/ or raw/failed/, remove the
original from raw/ so raw/ only holds unprocessed input. The .processed /
.failed marker is now only a fallback when the removal itself fails.
Existing markers are still honoured.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ingestion/internal/watcher/watcher_test.go

@@ -89,13 +89,12 @@ func TestStart_ProcessesFile(t *testing.T) {
 	}
 	require.True(t, found, "file should be copied to processed/")
 
-	// Original file should still exist (copy, not move — keeps Obsidian vault intact).
+	// Inbox zero: once archived, the original leaves raw/ and no marker is
+	// left behind, so what remains in raw/ is exactly the unprocessed set.
 	_, err := os.Stat(rawFile)
-	assert.NoError(t, err, "original file should remain in raw/")
-
-	// A .processed marker should exist next to the original.
+	assert.ErrorIs(t, err, os.ErrNotExist, "original should be removed from raw/ once archived")
 	_, err = os.Stat(rawFile + ".processed")
-	assert.NoError(t, err, ".processed marker should be written")
+	assert.ErrorIs(t, err, os.ErrNotExist, "no .processed marker: the archive copy is the record")
 
 	// Wiki page should exist.
 	wikiPath := filepath.Join(brainDir, "wiki", "sources", "shape-up-book.md")
@@ -142,13 +141,11 @@ func TestStart_MovesToFailedOnError(t *testing.T) {
 	}
 	require.True(t, found, "file should be copied to failed/")
 
-	// Original file should still exist (copy, not move — keeps Obsidian vault intact).
+	// Inbox zero: a quarantined original leaves raw/ too, no marker beside it.
 	_, err := os.Stat(rawFile)
-	assert.NoError(t, err, "original file should remain in raw/")
-
-	// A .failed marker should exist next to the original.
+	assert.ErrorIs(t, err, os.ErrNotExist, "original should be removed from raw/ once quarantined")
 	_, err = os.Stat(rawFile + ".failed")
-	assert.NoError(t, err, ".failed marker should be written")
+	assert.ErrorIs(t, err, os.ErrNotExist, "no .failed marker: failed/ is the record")
 
 	// log.md should contain a watcher error entry.
 	logContent, err := os.ReadFile(filepath.Join(brainDir, "log.md"))