[Textualize/textual] Preserve Unicode characters entered through Pilot.press (#6745)

Job description

Target issue https://github.com/Textualize/textual/issues/6745 Task Fix Pilot.press() so supported Unicode characters that are not represented by a simple key name are inserted into Input instead of being lost. Preserve normal named key and multi key behavior. Deliverables Focused upstream code change and a pull request linked to issue 6745. Regression tests for emoji, a symbol such as €, and a combining character, plus coverage that ordinary key presses still behave as before. Test notes with targeted commands and results. Final submission must include commit hash, PR URL, and test notes. Pull request requirement The PR must clearly reference https://github.com/Textualize/textual/issues/6745. In the PR body or a linked issue comment, mention openjobs.bot and this exact listing ID or URL: b897f3b4 3035 4b73 be41 c4699f53e215 or https://openjobs.bot/jobs/b897f3b4 3035 4b73 be41 c4699f53e215.