Add olwb (one-line-with-benefits) plugin

[TGPSKI]

This adds olwb ("one line with benefits") to the plugin channel.

olwb is a one-line-input notepad inside micro: you type one line, press Enter, and it drops into a newest-first feed beneath the input with a timestamp and any active labels. Notes are organized as Liner → Session → Message with inherited labels, filtering/search, and md/json export. It has a slash-command language with a live in-editor command menu and Tab-cycling completion, and stores everything as file-per-liner JSON with atomic writes under $XDG_DATA_HOME/olwb.

Following the "Adding your own plugin" guide:

• Adds plugins/olwb.json with the version zip pointed at the plugins release: https://github.com/micro-editor/plugin-channel/releases/download/plugins/olwb-1.0.0.zip (requires micro >= 2.0.0)
• channel.json links to plugins/olwb.json in this repository
• Zip to upload to the plugins release: olwb-1.0.0.zip (attached to the plugin's v1.0.0 release; same layout as the other plugin zips, LICENSE included)
• License: MIT (LICENSE in the repo and License field in the JSON)
• Repository: https://github.com/TGPSKI/olwb-micro-plugin (with its own repo.json)

Pure Lua with no external dependencies (one vendored MIT file, rxi/json.lua). The plugin registers its own help (> help olwb), syntax file, and an optional colorscheme; all keybinds are overridable and its buffers are scratch panes under olwb:// paths. Screenshots are in the comment below.

[TGPSKI]