Update openspec with clarified design decisions

openspec/changes/declpac-cli-tool/specs/pacman-query/spec.md

@@ -0,0 +1,22 @@
+## ADDED Requirements
+
+### Requirement: Query pacman package database via libalpm
+
+The system SHALL use libalpm for fast local queries against the pacman
+package database.
+
+#### Scenario: Query installed packages
+- **WHEN** needing list of currently installed packages
+- **THEN** query via libalpm alpm_list_get(ALPM_LIST_PACKAGES)
+
+#### Scenario: Query available packages
+- **WHEN** validating package exists in pacman repos
+- **THEN** query via libalpm alpm_db_get_pkg()
+
+#### Scenario: Check database last sync time
+- **WHEN** checking if database needs refresh
+- **THEN** check /var/lib/pacman/db.lock timestamp
+
+#### Scenario: Query foreign packages
+- **WHEN** checking if package is AUR-installed
+- **THEN** query via libalpm alpm_db_get_pkg(ALPM_DB_TYPE_LOCAL)