vault-fetch: fix multiline secret values being truncated

The read-based loop split multiline values on newlines, causing only
the first line to be written. Use jq -j to write each key's value
directly to files, preserving multiline content.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/vault-fetch/vault-fetch.sh

@@ -137,9 +137,9 @@ fetch_from_vault() {
 
     # Write each secret key to a separate file
     log "Writing secrets to $OUTPUT_DIR"
-    echo "$SECRET_DATA" | jq -r 'to_entries[] | "\(.key)\n\(.value)"' | while read -r key; read -r value; do
-        echo -n "$value" > "$OUTPUT_DIR/$key"
-        echo -n "$value" > "$CACHE_DIR/$key"
+    for key in $(echo "$SECRET_DATA" | jq -r 'keys[]'); do
+        echo "$SECRET_DATA" | jq -j --arg k "$key" '.[$k]' > "$OUTPUT_DIR/$key"
+        echo "$SECRET_DATA" | jq -j --arg k "$key" '.[$k]' > "$CACHE_DIR/$key"
         chmod 600 "$OUTPUT_DIR/$key"
         chmod 600 "$CACHE_DIR/$key"
         log "  - Wrote secret key: $key"