Adds lua/whipsmart/plugins/markdown.lua as an opt-in extra that bundles
render-markdown.nvim (unconditional) and obsidian.nvim + blink.compat
(gated on vim.g.obsidian_vaults being set in local.lua). Uses
blink.cmp.config.merge_with to extend the completion config post-setup
with markdown-specific per_filetype sources and [[wikilink trigger behaviour.
Also fixes a load-order bug where pcall(require, 'local') ran before
vim.g.have_nerd_font and all vim.o.* defaults were set, making it
impossible for local.lua to override them. The call is now at the end
of Section 1 so local.lua runs last and overrides work correctly.
UNIFIED.md updated: markdown extra documented, roci migration and
load-order fix checked off the roadmap.
Geoff Cheshire