* refactor(config): replace array preset syntax with preset_name = true
Problem: setup() mixed array entries (preset names) and hash entries
(custom providers keyed by filetype), requiring verbose
vim.tbl_deep_extend boilerplate to override presets.
Solution: unify under a single key=value model. Keys are preset names
or filetypes; true registers the preset as-is, a table deep-merges
with the matching preset (or registers a custom provider if no preset
matches), and false is a no-op. Array entries are dropped. Also adds
-f gfm to presets.github args so pandoc parses input as GFM.
* ci: format
* fix(presets): parenthesize gsub output to suppress redundant-return-value
* ci: remove superfluous things
* refactor: remove PreviewWatch* events and clean up docs
Problem: PreviewWatchStarted/PreviewWatchStopped were redundant with
the status() API, and the doc had a wrong author, stale INSTALLATION
format, and "watch mode" language left over from the watch → toggle
rename.
Solution: Remove the events and their tests. Fix the doc author,
rename INSTALLATION → SETUP to match sibling plugins, replace "watch
mode" with "auto-compile" throughout, and drop the events from EVENTS.
0b16ff7178