build: modernize repository (#27)

* build: clean up gitignore and remove empty gitmodules

Problem: .gitignore contained 48 lines of C/shared-object boilerplate
irrelevant to a Lua Neovim plugin. .gitmodules was tracked but empty.

Solution: replace .gitignore with minimal entries covering only files
this project actually produces. Delete the vestigial .gitmodules.

* build: add editorconfig and prettierrc

Problem: no editor or formatter configuration, inconsistent with
cp.nvim and diffs.nvim conventions.

Solution: add .editorconfig (2-space Lua indent, utf-8, final newline)
and .prettierrc (prose wrap, 80 cols, single quotes, no semi) matching
the other repos.

* build: add Makefile for lint and test targets

Problem: .github/pre-commit calls `make fastlint` and .github/pre-push
calls `make lint && make test`, but no Makefile existed, so the git
hooks failed.

Solution: add Makefile with lint (stylua + selene), fastlint
(pre-commit), and test (luarocks test) targets.

* docs: add fork copyright to LICENSE

Problem: LICENSE only contained the original author's copyright notice.

Solution: add a second copyright line for the fork maintainer. MIT
requires retaining the original notice; adding a line for derivative
work is standard practice.

* ci: restructure workflows to quality/test/luarocks pattern

Problem: CI used a single tests.yml for linting, typechecking, and
testing. No conditional path filtering, no markdown format check, and
a stale mirror_upstream_prs.yml and duplicate luarocks.yml existed.

Solution: replace tests.yml with quality.yaml (stylua, selene,
lua-typecheck, prettier with dorny/paths-filter) and test.yaml
(nvim-busted, stable+nightly matrix). Update luarocks.yaml to
reference quality.yaml. Delete mirror_upstream_prs.yml and duplicate
luarocks.yml. Fix automation workflow sender check.

* build: rewrite issue templates

Problem: issue templates used upstream stevearc references, severity
dropdowns, outdated lazy.nvim bootstrap, and the .yml extension
inconsistent with other repos.

Solution: replace with .yaml templates matching cp.nvim/diffs.nvim
style. Bug report uses prerequisites checkboxes, checkhealth output,
modern lazy.nvim bootstrap with vim.g.oil pattern. Feature request
uses problem/solution/alternatives format. Add config.yaml to disable
blank issues and link discussions.

* docs: rewrite README

Problem: README contained upstream triage tables, severity dropdowns,
the old setup() pattern, a tree view question, and references to
stevearc/oil.nvim as the primary source.

Solution: full rewrite matching cp.nvim/diffs.nvim style with bold
tagline, features list, requirements, installation, documentation,
FAQ (lazy.nvim setup with vim.g.oil, migration guide, alternatives),
and acknowledgements crediting the original author.

* revert: remove Makefile

Problem: Makefile was added in b9279b5 but was previously deleted
intentionally.

Solution: remove it.

.github/workflows/test.yaml

@@ -0,0 +1,22 @@
+name: test
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        nvim: [stable, nightly]
+    name: Test (Neovim ${{ matrix.nvim }})
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: nvim-neorocks/nvim-busted-action@v1
+        with:
+          nvim_version: ${{ matrix.nvim }}