Add OpenSpec for declpac CLI tool

- OpenSpec for declarative pacman package management
- stdin and --state file inputs with merging
- Full system upgrades, transitive deps, orphan cleanup
- AUR support with pacman/makepkg fallback
- Machine-readable output for scripting

openspec/changes/declpac-cli-tool/specs/state-validation/spec.md

@@ -0,0 +1,17 @@
+## ADDED Requirements
+
+### Requirement: Can detect empty state input
+
+The system SHALL detect when no packages are provided in any input source.
+
+#### Scenario: Empty state warning
+- **WHEN** no package names are found in stdin or state files
+- **THEN** system shall print a warning to stderr
+
+#### Scenario: Empty state warning message
+- **WHEN** warning is printed for empty state
+- **THEN** message shall say: "Called without state, aborting.."
+
+#### Scenario: Abort on empty state
+- **WHEN** empty state is detected
+- **THEN** system shall exit with code 1 (error: no packages to sync)