Quote table and view names when preparing LLM context

[hao0x1]

Description

A table named products 1 is valid in SQLite, but it makes \llm fail with near "1": syntax error while preparing sample rows. The query uses the table name without quoting it.

This quotes table and view names and escapes any double quotes inside them. The new tests use real SQLite databases with spaces, reserved words, quotes, and dots in object names. Only the external LLM command is mocked.

Related to #253. This reproduces the same error, although I couldn't check the reporter's database to confirm its cause.

The suite passes on Python 3.10 and 3.13, including runs with and without SQLean: 238 passed, with the same skips and expected/unexpected failures as main. tox -e style passes with the Ruff version pinned in CI. Type checking passes for the changed files; the full check still reports the same five existing diagnostics as main.

Codex helped with the patch and tests.

Checklist

• I've added this contribution to the CHANGELOG.md file.