feat: Implement SQLite infrastructure layer for persistent storage

[cyrusagent]

Summary

Implements a complete SQLite persistence layer for the Logseq application following the design outlined in PER-12. This provides durable, local-first storage for Page aggregates and their associated Block hierarchies.

Changes Made

1. Database Schema (schema.rs)

• 5 normalized tables with proper indexing and foreign key constraints:
  • pages: Page metadata (id, title, timestamps)
  • blocks: Block content with hierarchical parent_id references
  • block_children: Junction table for maintaining child order
  • urls: Extracted URLs from block content
  • page_references: Page references and tags
• All tables use CASCADE delete for referential integrity
• Idempotent initialization for safe repeated calls

2. Repository Implementation (sqlite_page_repository.rs)

• SqlitePageRepository: Complete implementation of PageRepository trait
  • In-memory and file-based database support
  • Atomic transactions for all mutations
  • Two-pass block insertion to satisfy foreign key constraints:
    1. Insert all blocks (sorted by indent level)
    2. Insert block_children relationships
• Full serialization/deserialization of complex Page aggregates
• Proper error handling with conversion to DomainError

3. Dependencies

• Added rusqlite v0.32 with bundled SQLite for portability

4. Testing

• 11 comprehensive tests covering:
  • Schema initialization and idempotency
  • CRUD operations (save, find_by_id, find_by_title, find_all, delete)
  • Update/upsert functionality
  • Complex block hierarchies (3+ levels deep)
  • URL and page reference preservation
  • Edge cases (non-existent records)

Test Results

Summary: 172 tests run: 172 passed, 12 skipped

All persistence tests pass, including:

• test_block_hierarchy_preserved
• test_urls_and_references_preserved
• test_save_and_find_by_id
• test_update_page

Technical Highlights

• Foreign key constraint handling: Blocks are sorted by indent level before insertion to ensure parents exist before children
• Two-pass insertion strategy: Avoids FK violations in block_children table
• Transaction safety: All write operations wrapped in transactions
• Clean architecture: Follows existing patterns from QdrantVectorStore

Next Steps

• Integration with application services (ImportService, SyncService)
• Migration from in-memory to SQLite-backed repositories
• Optional: Add full-text search with FTS5

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