ci: add ShellCheck, shfmt, and editorconfig-checker

.editorconfig

@@ -0,0 +1,23 @@
+# http://editorconfig.org
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.json]
+insert_final_newline = ignore
+
+[Makefile]
+indent_style = tab
+
+# Shell scripts — shfmt reads these properties
+[*.sh]
+switch_case_indent = true
+
+[*.md]
+trim_trailing_whitespace = false

.github/workflows/check.yaml

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+name: check
+
+on:
+  push:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref == 'refs/heads/main' && github.sha || github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Find bash scripts
+        id: find-bash
+        run: |
+          bash_files=""
+          # .sh files with bash shebangs
+          for f in $(find . -name '*.sh' -not -path './.git/*' -not -path './node_modules/*'); do
+            shebang=$(head -1 "$f")
+            if echo "$shebang" | grep -qE '(bash|^#!/bin/sh)'; then
+              bash_files="$bash_files $f"
+            fi
+          done
+          # bin/ scripts without .sh extension
+          for f in $(find ./bin -maxdepth 1 -type f -not -name '*.sh' -not -path './.git/*'); do
+            shebang=$(head -1 "$f")
+            if echo "$shebang" | grep -qE '(bash|^#!/bin/sh)'; then
+              bash_files="$bash_files $f"
+            fi
+          done
+          echo "files=$bash_files" >> "$GITHUB_OUTPUT"
+          echo "Found bash files:$bash_files"
+
+      - name: ShellCheck
+        if: steps.find-bash.outputs.files != ''
+        run: |
+          bash_files="${{ steps.find-bash.outputs.files }}"
+          echo "Running ShellCheck on:$bash_files"
+          shellcheck $bash_files
+
+      - name: shfmt check
+        if: steps.find-bash.outputs.files != ''
+        run: |
+          bash_files="${{ steps.find-bash.outputs.files }}"
+          echo "Running shfmt on:$bash_files"
+          # -d shows diff; indent settings sourced from .editorconfig
+          shfmt -d $bash_files
+
+      - name: EditorConfig check
+        uses: editorconfig-checker/action-editorconfig-checker@main
+
+      - name: Run editorconfig-checker
+        run: editorconfig-checker

.shellcheckrc

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+# ShellCheck configuration for nsheaps/git-wt
+# https://www.shellcheck.net/wiki/
+
+# Default shell dialect — all scripts in this repo are bash.
+shell=bash
+
+# SC1091: Not following sourced files — sourced paths are dynamic
+disable=SC1091
+
+# SC2034: Variable appears unused — some variables are used in tests or exported
+disable=SC2034