Add CI typo check (#9)

Runs crate-ci/typos on every push to main and every pull request.
Catches prose and code typos before they land in blog posts or slides.

Config in .typos.toml allowlists HED/hed (Hierarchical Event
Descriptors, not a typo of HEAD) and skips bundled presentation
assets and lock files.

Closes #8

Author: neuromechanist

.github/workflows/typos.yml

@@ -0,0 +1,19 @@
+name: typos
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  typos:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Check typos
+        uses: crate-ci/typos@master
+        with:
+          config: ./.typos.toml

.typos.toml

@@ -0,0 +1,15 @@
+[default.extend-words]
+# Hierarchical Event Descriptors (HED) is a domain acronym used throughout
+# the course. typos confuses it with HEAD. Preserve the exact casing.
+HED = "HED"
+hed = "hed"
+
+[files]
+# Skip bundled third-party artifacts and lock files.
+extend-exclude = [
+  "presentations/**/assets/**",
+  "**/dist/**",
+  "**/node_modules/**",
+  "**/*.lock",
+  "**/bun.lock",
+]