feat(cli): Comprehensive UI/UX Overhaul & Alternate Screen Layout

[arjun-vegeta]

Description

This PR implements a comprehensive overhaul of the Loopcode CLI's UI/UX to address positioning, overlapping, and scrolling issues present in the current terminal output. By moving away from native scrollback and implementing a managed viewport with an alternate screen buffer, the CLI now behaves like a true terminal IDE.

Key Features

• Alternate Screen Buffer: Bound the CLI layout perfectly to the terminal window size to prevent layout breaking upon overflow.
• Virtualized Scrolling: Implemented raw internal log scrolling using stdin mouse scroll intercepts.
• Bracketed Paste Mode: Added full support for multi-line pastes, directly parsing \x1b[200~ escape sequences to prevent rendering stutter.
• Large Prompt Squashing: Long prompt outputs are visually truncated in the chat UI to save vertical space.
• AST-Cached Markdown Renderer: Introduced a fast-path Regex and abstract syntax tree caching to eliminate React reconciliation lag during fast scrolling.
• Overlay Dialogs (Z-Index): The SessionPicker is now rendered as a true floating absolute-positioned overlay, pausing main input listeners properly to avoid conflicts.
• Structured Diffs: Git patches are now cleanly parsed and rendered with line numbers visually similar to GitHub's PR viewer.
• Visual Token Telemetry: The Status Bar now includes a dynamic budget progress bar.
• Theming System: <ThemedBox> and <ThemedText> ensure a cohesive design language across the CLI.

Validation

All format, lint, typecheck, and unit test pipelines are fully passing.