#8741: fix(tui): allow j/k keys to be typed in search inputs (#7378)

Remove vim-style j/k navigation from FilterableSelectList and SearchableSelectList components. These keys were mapped to up/down navigation when the search input was empty, preventing users from searching for models or sessions starting with 'j' or 'k'. Users can still navigate using arrow keys or Ctrl+P/Ctrl+N. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR removes vim-style `j/k` navigation from two TUI list components (`FilterableSelectList` and `SearchableSelectList`) so users can type model/session names beginning with `j` or `k` in the search/filter input. Navigation remains available via arrow keys and `Ctrl+P`/`Ctrl+N`, aligning input handling with the stated UX goal while keeping the rest of the selection and filtering behavior unchanged. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - Changes are narrowly scoped to key handling in two TUI components, simply removing `j/k` from navigation and leaving arrow/Ctrl bindings intact; no state management, filtering, or rendering logic was altered beyond removing the conditional `allowVimNav` branches. - No files require special attention <!-- greptile_other_comments_section --> _{(4/5) You can add custom instructions or style guidelines for the agent [here](https://app.greptile.com/review/github)!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->