Implements comprehensive tag/label functionality for variables:
## Core Features
- Tags: key-value pairs with same-key override semantics
- Labels: bare identifiers
- Deletion syntax: `:name` removes tag or label
- Mutual exclusion: tag keys and label names cannot coexist
- Unified `var tag` command for all tag/label operations
## Data Model
- Extended Variable type with tags/labels fields
- New variable_tags and variable_labels SQLite tables
- Foreign key constraints with CASCADE delete
- Proper indexes for efficient querying
## Query Capabilities
- Filter by scope (hierarchical prefix matching)
- Filter by tags (key:value pairs, AND logic)
- Filter by labels (bare names, AND logic)
- Combined filtering (scope + tags/labels)
## CLI Commands
- `json-cas var create --tag <tag>...` - initial tags/labels
- `json-cas var tag <id> <tag>...` - add/update/delete
- `json-cas var list --tag <tag>...` - query with filters
## Implementation Details
- TagLabelConflictError and InvalidTagFormatError types
- Atomic batch operations with rollback
- 46 comprehensive tests for tags/labels
- Backward compatible with Phase 1
- All 214 tests pass
Closes#22
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
xiaoju