[IMP] add structured logging functions

Add logging functions to lib/common.sh for consistent output formatting:
- log_info(): Standard informational messages with [INFO] prefix
- log_warn(): Warning messages to stderr with [WARN] prefix
- log_error(): Error messages to stderr with [ERROR] prefix
- log_step(): Section headers with visual separators

Update upgrade.sh to use these functions throughout, replacing ad-hoc
echo statements. This provides:
- Consistent visual formatting across all scripts
- Clear distinction between info, warnings and errors
- Errors properly sent to stderr
- Easier log parsing and filtering

Also removed redundant '|| exit 1' statements since set -e handles
command failures automatically.

lib/common.sh

@@ -9,6 +9,11 @@ set -euo pipefail
 readonly DATASTORE_PATH="/srv/datastore/data"
 readonly FILESTORE_SUBPATH="var/lib/odoo/filestore"
 
+log_info()  { printf "[INFO]  %s\n" "$*"; }
+log_warn()  { printf "[WARN]  %s\n" "$*" >&2; }
+log_error() { printf "[ERROR] %s\n" "$*" >&2; }
+log_step()  { printf "\n===== %s =====\n" "$*"; }
+
 query_postgres_container() {
     local query="$1"
     local db_name="$2"
@@ -58,4 +63,5 @@ exec_python_script_in_odoo_shell() {
 }
 
 export DATASTORE_PATH FILESTORE_SUBPATH
+export -f log_info log_warn log_error log_step
 export -f query_postgres_container copy_database copy_filestore exec_python_script_in_odoo_shell