Text file editor tool plugin

[linuztx]

• Added text_editor tool plugin: read, write, patch with numbered lines
• Native read/write/patch tools for text files with line numbers
• Token budgeting: long line cropping, total-read limit, warning messages when content is trimmed
• Binary detection and reject with a clear terminal message
• Insert/replace/delete edits in a single patch
• Mtime tracking so patches require a prior read and reject when the file changed
• In-place patch optimization: allow consecutive patches without re-read when each edit replaces N lines with N lines
• Enforce re-read after insert, delete, or N≠M replace to avoid line-number drift
• Overlap and overflow validation for edits
• Stream patch application to a temp file to avoid loading large files fully into RAM
• Extension hooks: read_after, write_before/after, patch_before/after
• Config UI: max line tokens, default line count, max total read tokens
• Compress prompts for tokens and direct agents to use the terminal for search/replace