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-files/spec.md

@@ -0,0 +1,21 @@
+## ADDED Requirements
+
+### Requirement: Can load package states from state files
+
+The system SHALL load package lists from state files specified via --state flag.
+
+#### Scenario: Single state file loading
+- **WHEN** a state file is provided via --state flag
+- **THEN** system shall read package names from the file content
+
+#### Scenario: Multiple state file loading
+- **WHEN** multiple --state flags are provided
+- **THEN** system shall load package names from each file
+
+#### Scenario: State file format is text list
+- **WHEN** loading from state files
+- **THEN** system shall parse whitespace-delimited package names
+
+#### Scenario: File path validation
+- **WHEN** a state file path points to a non-existent file
+- **THEN** system shall report a file read error