minimal CI checks (#2)

Example output:

```
> ./scripts/validate-proposals.sh
OK: 0001-init.md
ERROR: Invalid filename: 0002.md
  Expected format: NNNN-name.md (e.g., 0007-my-proposal.md)
OK: 0003-example.md
OK: 0003-example2.md
ERROR: Invalid filename: lol.txt
  Expected format: NNNN-name.md (e.g., 0007-my-proposal.md)
ERROR: Duplicate ID 0003 found in: 0003-example.md 0003-example2.md
```

---------

Signed-off-by: Andrew Duffy <andrew@a10y.dev>

Author: a10y

.github/workflows/validate-proposals.yml

@@ -0,0 +1,17 @@
+name: Validate Proposals
+
+on:
+  pull_request:
+    branches:
+      - develop
+
+jobs:
+  validate-naming:
+    name: Validate proposal naming convention
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Validate proposal file names
+        run: ./scripts/validate-proposals.sh

scripts/validate-proposals.sh

@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+validate_file() {
+  local filename="$1"
+
+  # Check if file matches the expected pattern: NNNN-*.md
+  if ! echo "$filename" | grep -qE '^[0-9]{4}-[a-zA-Z0-9_-]+\.md$'; then
+    echo "ERROR: Invalid filename: $filename"
+    echo "  Expected format: NNNN-name.md (e.g., 0007-my-proposal.md)"
+    return 1
+  fi
+
+  return 0
+}
+
+exit_code=0
+valid_ids=""
+
+# Find all files in proposals/ directory (if it exists)
+if [ -d "proposals" ]; then
+  for file in $(ls proposals/ | sort); do
+    file="proposals/$file"
+    # Skip if no files match (glob returns literal pattern)
+    [ -e "$file" ] || continue
+
+    filename=$(basename "$file")
+
+    if validate_file "$filename"; then
+      echo "OK: $filename"
+      # Collect ID and filename for duplicate checking
+      id="${filename:0:4}"
+      valid_ids="${valid_ids}${id} ${filename}"$'\n'
+    else
+      exit_code=1
+    fi
+  done
+
+  # Check for duplicate IDs
+  duplicate_ids=$(echo "$valid_ids" | awk '{print $1}' | sort | uniq -d)
+  if [ -n "$duplicate_ids" ]; then
+    for dup_id in $duplicate_ids; do
+      files=$(echo "$valid_ids" | grep "^$dup_id " | awk '{print $2}' | tr '\n' ' ')
+      echo "ERROR: Duplicate ID $dup_id found in: $files"
+    done
+    exit_code=1
+  fi
+fi
+
+exit $exit_code