Create internal/zellij package for terminal multiplexer abstraction

[newhook]

Summary

This PR extracts all zellij terminal multiplexer code from internal/claude/runner.go into a dedicated internal/zellij/ package. The new package provides clean abstractions for session, tab, and pane management with proper typing and error handling.

Key changes:

• Created internal/zellij/zellij.go with a type-safe Client struct and comprehensive API
• Refactored internal/claude/runner.go to use the new zellij package
• Removed ~165 lines of duplicated zellij command code from runner.go
• Added unit tests for the new package

New Package API

The internal/zellij package provides:

Session Management

• ListSessions() - List all zellij sessions
• SessionExists() - Check if a session exists
• CreateSession() - Create a new session (detached)
• EnsureSession() - Create session if it doesn't exist

Tab Management

• CreateTab() - Create a new tab with name and working directory
• SwitchToTab() - Switch to a tab by name
• QueryTabNames() - List all tab names in a session
• TabExists() - Check if a tab exists
• CloseTab() - Close the current tab

Pane Input Control

• WriteASCII() - Write ASCII codes (Ctrl+C, Enter, etc.)
• WriteChars() - Write text to the pane
• SendCtrlC() - Convenience method for interrupt
• SendEnter() - Convenience method for enter key
• ExecuteCommand() - Write command and send Enter

High-Level Operations

• TerminateProcess() - Send Ctrl+C twice with delay for reliable termination
• ClearAndExecute() - Clear line and run a command
• TerminateAndCloseTab() - Terminate process and close tab

Benefits

• Single source of truth for all zellij interactions
• Type-safe API instead of raw exec.Command calls scattered throughout the codebase
• Testable - The client can be mocked for unit testing
• Consistent error handling with wrapped errors
• Configurable timeouts via the Client struct
• Reusable across the codebase

Issues Resolved

• ac-8qe: Create internal/zellij package (Epic)
  • ac-gn0: Create zellij package structure with Client struct and core types
  • ac-8hf: Implement zellij session management functions
  • ac-t6g: Implement zellij tab management functions
  • ac-4fu: Implement zellij pane input control functions
  • ac-ql4: Implement high-level zellij operations
  • ac-8ev: Refactor claude/runner.go to use zellij package
  • ac-0by: Add unit tests for zellij package

Test Plan

• Unit tests pass: go test ./internal/zellij/...
• Full test suite passes: go test ./...
• Build succeeds: go build -o co .
• Manual testing: Create and run work units with zellij integration

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