feat(ui): add configurable input panel max rows and horizontal scrolling

- Introduce `ui.input_max_rows` (default 5) to control how many rows the input panel expands before scrolling.
- Bump `CONFIG_SCHEMA_VERSION` to **1.2.0** and update migration documentation.
- Update `configuration.md` and migration guide to describe the new setting.
- Adjust TUI height calculation to respect `input_max_rows` and add horizontal scrolling support for long lines.
- Add `unicode-segmentation` dependency for proper grapheme handling.

docs/configuration.md

@@ -64,6 +64,9 @@ These settings customize the look and feel of the terminal interface.
 -   `wrap_column` (integer, default: `100`)
     The column at which to wrap text if `word_wrap` is enabled.
 
+-   `input_max_rows` (integer, default: `5`)
+    The maximum number of rows the input panel will expand to before it starts scrolling internally. Increase this value if you prefer to see more of long prompts while editing.
+
 ## Storage Settings (`[storage]`)
 
 These settings control how conversations are saved and loaded.

docs/migrations/README.md

@@ -2,6 +2,10 @@
 
 Owlen is still in alpha, so configuration and storage formats may change between releases. This directory collects short guides that explain how to update a local environment when breaking changes land.
 
+### Schema 1.2.0 (November 2025)
+
+`config.toml` now records `schema_version = "1.2.0"` and introduces the optional `ui.input_max_rows` setting. The new key defaults to `5`, so no manual edits are required unless you prefer a taller input panel. Existing files are updated automatically on load/save.
+
 ### Schema 1.1.0 (October 2025)
 
 Owlen `config.toml` files now carry a `schema_version`. On startup the loader upgrades any existing file and warns when deprecated keys are present. No manual changes are required, but if you track the file in version control you may notice `schema_version = "1.1.0"` added near the top.