🚀 feat(query-history): append history queries without replacing

[Mrthnx]

Summary

This PR adds the ability to append a query from history to the editor without replacing the current text. Previously, selecting a query from history (via QueryHistoryScreen or Telescope) would overwrite whatever was in the editor. Now users can press a to append the selected query instead.

Motivation

When working with query history, it's common to want to reuse or combine previous queries. The existing behavior (<enter>) replaces the entire editor content, which is destructive if you're building a multi-statement query or referencing previous snippets. Appending provides a non-destructive alternative.

Changes

1. New _append_history_query() method

Added to QueryExecutionMixin (sqlit/domains/query/ui/mixins/query_execution.py):

• Appends the selected query to the end of the current editor text
• Adds a newline separator if the editor is not empty
• Preserves undo state via _push_undo_state()
• Moves cursor to the end of the appended text
• Focuses the query input

2. New append action in QueryHistoryScreen

Added to sqlit/domains/query/ui/screens/query_history.py:

• New key binding: a → action_append
• Updated footer shortcuts to show Append (a) alongside existing actions
• Returns ("append", entry) result to the caller

3. Handle append action in result handlers

Updated both _handle_history_result and _handle_telescope_result in QueryExecutionMixin to handle the new "append" action and delegate to _append_history_query().

How to test

1. Open Query History (H) or Telescope (Ctrl+T)
2. Write some text in the query editor (or leave it empty)
3. Navigate to a history entry and press a
4. The query should appear appended at the end of the editor, with proper newline separation

Keymap

Key	Action
<enter>	Select (replaces editor content)
a	Append (adds to editor content)
*	Toggle star
d	Delete entry