add query-pane-info action for JSON pane/tab information

[tennox]

Disclaimer: This PR has been developed with the help of Claude, but I've tested and reviewed manually.

Summary

• Added query-pane-info CLI command to retrieve structured information about the current pane and its containing
  tab
• Returns JSON-formatted output including tab name, tab index, pane ID, pane type, and pane name
• Enables programmatic inspection of zellij session state for automation and scripting

Changes

• New CLI Command: Added QueryPaneInfo action that uses ZELLIJ_PANE_ID environment variable
• JSON Output: Structured information format for easy parsing by external tools
• Searches across all tabs to locate the target pane
• Error Handling: Graceful handling of invalid/missing pane IDs with clear error messages
• Plugin API: Complete protobuf integration with QueryPaneInfoPayload
• Backward Compatible: No changes to existing functionality

Usage

# Get information about current pane (must be run within zellij session)
zellij action query-pane-info

Example Output:

{
  "tab_name": "Zellij Fork",
  "tab_index": 1,
  "pane_id": 42,
  "pane_type": "terminal",
  "pane_name": "hx src/main.rs"
}

Architecture

Follows the established pattern of QueryTabNames:

• Uses ZELLIJ_PANE_ID environment variable (consistent with other pane operations)
• Routes through standard CLI → Action → Route → Screen → ServerInstruction::Log flow
• Leverages existing tab iteration and pane lookup mechanisms
• JSON serialization using serde for structured output

Error Handling

• Missing Pane: Clear error message when pane ID not found in any tab
• Invalid Environment: Proper error when ZELLIJ_PANE_ID not set or malformed
• Type Safety: Converts between raw u32 and internal PaneId enum safely