Refactor main runtime into app modules

[forketyfork]

Summary

• split app runtime helpers into focused app modules (layout, input, grid nav, worktree, terminal actions)
• make main.zig a thin entrypoint delegating to app/runtime.zig
• update architecture docs to reflect new structure

Testing

• zig build
• zig build test

[Copilot]

Pull request overview

This PR refactors the monolithic main.zig file (1920+ lines) into focused modules within the app/ directory, improving code organization and maintainability. The main runtime logic is preserved but now properly separated by responsibility.

Changes:

• Split runtime helpers into focused modules: layout, input_text, input_keys, grid_nav, worktree, terminal_actions, and ui_host
• Transform main.zig into a thin entrypoint that delegates to app/runtime.zig
• Update architecture documentation to reflect new module structure

Reviewed changes

Copilot reviewed 12 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/main.zig	Simplified to 5-line entrypoint calling app/runtime.zig
src/app/runtime.zig	New 1227-line file containing main app lifecycle (extracted from main.zig)
src/app/layout.zig	Layout calculations: sizing, scaling, hover detection, terminal resize
src/app/ui_host.zig	UI host snapshot and mouse context helpers
src/app/grid_nav.zig	Grid navigation logic and notification formatting
src/app/input_keys.zig	Keyboard input encoding and modifier detection
src/app/input_text.zig	IME and text input handling
src/app/terminal_actions.zig	Terminal operations: clipboard, paste, clear
src/app/worktree.zig	Git worktree command builders and path escaping
src/shell.zig	Comment repositioning for chdir error handling
docs/architecture.md	Updated to reflect new app module structure
CLAUDE.md	Clarified std.mem.span vs std.mem.sliceTo usage

Files not reviewed (2)

• .idea/.gitignore: Language not supported
• .idea/zigbrains.xml: Language not supported

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