Add SQLite full-text search support

[anitnilay20]

Description

Implement SQLite FTS (Full-Text Search) capabilities with FTS4 and FTS5 support.

Requirements

• FTS virtual table creation
• FTS4 and FTS5 support
• Full-text query syntax
• Search result ranking
• Snippet and highlight generation
• Write comprehensive tests

Acceptance Criteria

• Complete FTS integration
• Support for both FTS4 and FTS5
• Search ranking and snippets
• Type-safe FTS queries

Files to create

• beatrix_core/src/relational/fts/sqlite.rs

Example Usage

#[derive(RelationalModel)]
#[fts_table(version = "fts5", content = "articles")]
struct ArticleFTS {
    title: String,
    content: String,
}

let results = ArticleFTS::search("rust programming")
    .with_snippets()
    .rank_by_relevance()
    .fetch_all(&db).await?;