chore(nvim): track project-local Neovim config, drop .idea from ignore

Add .nvim.lua, an opt-in project-local Neovim configuration for
LazyVim users. It extends the runtime path with .nvim/ so the
treesitter injections ship with the repo, and wires conform to
format embedded GraphQL regions (via prettier's injected formatter)
alongside goimports/gofumpt on Go buffers.

Add .nvim/queries/go/injections.scm, which marks Go raw string
literals starting with query/mutation/subscription/fragment as
GraphQL injections, so treesitter highlighting and formatting apply
to the embedded AniList queries.

Remove .idea from .gitignore: the ignore list now deliberately
tracks project-local editor configs (.nvim.lua) instead of
editor-specific junk.

.gitignore

@@ -30,7 +30,6 @@ frontend/package.json.md5
 # Root-level lockfile only: the frontend lockfile IS tracked so CI installs
 # are reproducible and setup-node's npm cache has something to hash.
 /package-lock.json
-.idea
 .env
 environment.go
 # Updater signing private key. The public half (updater.pub) is committed and