feat(prompts): implement Phase 1 - Foundation (FR-1)

Implement addressable artifacts with content-based identity and change detection.

Core Features:
- Artifact model with SHA-256 content digests
- ArtifactReference for cross-space addressing
- IArtifactRepository interface for pluggable storage
- SQLiteArtifactRepository implementation
- ArtifactService for high-level operations
- Content digest calculation utilities

Database:
- prompt_artifacts table with indexes
- Support for artifact metadata and types
- UNIQUE constraint on space_id+name

Tests (41 passing):
- 26 model tests (metadata, artifacts, references, digests)
- 15 repository tests (CRUD, queries, constraints)

Implements:
- FR-1.1: Unique addressability by name and ID
- FR-1.2: Content digest computation and storage
- FR-1.3: Cross-space artifact references

Files Created:
- markitect/prompts/models.py
- markitect/prompts/repositories/interfaces.py
- markitect/prompts/repositories/sqlite.py
- markitect/prompts/services/artifact_service.py
- migrations/prompts/001_create_artifacts_table.sql
- tests/unit/prompts/test_artifact_models.py
- tests/unit/prompts/test_artifact_repository.py

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

markitect/prompts/__init__.py

@@ -0,0 +1,33 @@
+"""
+Prompt Dependency Resolution system for MarkiTect.
+
+This package provides infrastructure for executing PromptTemplates with
+deterministic dependency resolution, incremental recomputation, and quality
+validation across InformationSpaces.
+
+Key components:
+- Artifact management with content-based addressing
+- Template definition with macro support
+- Deterministic resolution across spaces
+- Idempotent execution with InputBundleHash
+- Dependency graph construction and tracking
+- Incremental recomputation with change impact analysis
+- Quality gate validation and halting policies
+- Complete traceability and provenance tracking
+"""
+
+__version__ = "0.1.0"
+
+from markitect.prompts.models import (
+    Artifact,
+    ArtifactReference,
+    ArtifactMetadata,
+    ArtifactType,
+)
+
+__all__ = [
+    "Artifact",
+    "ArtifactReference",
+    "ArtifactMetadata",
+    "ArtifactType",
+]