feat: add backend SQL construction service and fix query result display

[Blankll]

Summary

Moves all SQL construction (wrapping, filtering, sorting, pagination) from the frontend to the backend with proper sqlparser-based parsing and validation.

Changes

sql_service.rs (new)

Centralized SQL construction service. Handles:

• Stripping trailing semicolons and -- comments before wrapping
• Parsing with sqlparser to validate single SELECT/WITH statements
• Injecting schema qualification on unqualified table references
• Building WHERE/ORDER BY/LIMIT clauses from structured data
• Rejecting multi-statement or DML input with clear error messages

QueryResultPanel.vue

• Removed buildWrappedSql — frontend no longer constructs SQL strings
• Sends structured sort/filter state to new execute_sorted_query command
• Backend derives database type from active connection

DataGrid.vue

• Fixed virtual scroller: column header moved outside scroll container
  so rows are never hidden behind the sticky header
• Added hideBatchActions prop to suppress batch action bar in query
  result panel

useSqlStatements.ts

• Replaced line-based + regex statement parser with a character-based
  state machine that tracks quotes, backticks, and comments
• Fixes false splitting of correlated subqueries like
  (SELECT count(*) FROM t WHERE x = y) as alias

search.rs

• UUID columns use ::text cast instead of CAST(... AS TEXT)
• Added exact-match optimization for UUID-formatted search terms
• JSON/JSONB columns also use ::text for compatibility

Testing

• 14 new unit tests for sql_service.rs covering: trailing semicolons,
  comments, multi-statement rejection, DML rejection, schema injection,
  filter/sort/pagination, MySQL and SQL Server dialects
• All 286 existing Rust tests pass
• All 416 frontend tests pass