feat(display): configurable tool preview length -- show full paths by default (#3841)

Tool call previews (paths, commands, queries) were hardcoded to truncate
at 35-40 chars across CLI spinners, completion lines, and gateway progress
messages. Users could not see full file paths in tool output.

New config option: display.tool_preview_length (default 0 = no limit).
Set a positive number to truncate at that length.

Changes:
- display.py: module-level _tool_preview_max_len with getter/setter;
  build_tool_preview() and get_cute_tool_message() _trunc/_path respect it
- cli.py: reads config at startup, spinner widget respects config
- gateway/run.py: reads config per-message, progress callback respects config
- run_agent.py: removed redundant 30-char quiet-mode spinner truncation
- config.py: added display.tool_preview_length to DEFAULT_CONFIG

Reported by kriskaminski

hermes_cli/config.py

@@ -285,6 +285,7 @@ DEFAULT_CONFIG = {
         "show_cost": False,       # Show $ cost in the status bar (off by default)
         "skin": "default",
         "tool_progress_command": False,  # Enable /verbose command in messaging gateway
+        "tool_preview_length": 0,  # Max chars for tool call previews (0 = no limit, show full paths/commands)
     },
 
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