Add query formatting from the leader menu

[Maxteabag]

Summary

• add an undoable SQL formatting action powered by the existing sqlparse dependency
• expose it as <space>p / Format Query in the leader menu
• uppercase SQL keywords, reindent clauses and lists, and add operator spacing
• preserve comments, strings, placeholders, semicolon boundaries, and sqlit’s two-blank-line boundaries
• remap the cursor beside the same SQL token after whitespace changes
• expose the action in generated help and the customizable keymap template

Fixes #278.

Why sqlparse

sqlparse is already a sqlit dependency, BSD licensed, lightweight, and non-validating. It formats without adding a new runtime or external executable. It is intentionally treated as a generic formatter rather than a dialect validator.

Validation

• 18 dedicated formatting unit/UI regressions
• 81 focused formatting, leader, state, and keymap tests passed
• full unit and UI suite: 1,477 passed, 2 skipped
• real Textual <space>p dispatch, undo, and cursor-token tests
• PostgreSQL JSON operators, MSSQL bracketed identifiers/hints, placeholders, comments, strings, multiple statements, and idempotence covered
• Ruff and structured autoreview: clean

This PR is intentionally left open for manual review.