docs: add OpenCode AI-assisted development guide (#2384)

Adds OpenCode support for AI-assisted development, including custom
commands and skills to help contributors maintain consistency and
streamline common workflows.

#### Changes
- Added "AI-Assisted Development with OpenCode" section to
CONTRIBUTING.md with:
  - Installation instructions and provider configuration
- Documentation for 8 custom commands (/implement, /continue,
/interview, /document, /commit, /create-plan, /create-scratch,
/create-justification)
  - Typical workflow guide
- Clear policy that AI-generated code must be reviewed before submission
- Added .agents/ directory for plans, scratches, and justifications
- Added .opencode/ commands and skills for the agent
- Added helper scripts for creating agent files

scripts/utils/generate-id.ts

@@ -0,0 +1,84 @@
+/**
+ * Generates a unique identifier using three simple words.
+ * Falls back to unix timestamp if word generation fails.
+ */
+export const generateId = (): string => {
+  const adjectives = [
+    'happy',
+    'bright',
+    'swift',
+    'calm',
+    'bold',
+    'clever',
+    'gentle',
+    'quick',
+    'sharp',
+    'warm',
+    'cool',
+    'fresh',
+    'solid',
+    'clear',
+    'sweet',
+    'wild',
+    'quiet',
+    'loud',
+    'smooth',
+  ];
+
+  const nouns = [
+    'moon',
+    'star',
+    'ocean',
+    'river',
+    'forest',
+    'mountain',
+    'cloud',
+    'wave',
+    'stone',
+    'flower',
+    'bird',
+    'wind',
+    'light',
+    'shadow',
+    'fire',
+    'earth',
+    'sky',
+    'tree',
+    'leaf',
+    'rock',
+  ];
+
+  const colors = [
+    'blue',
+    'red',
+    'green',
+    'yellow',
+    'purple',
+    'orange',
+    'pink',
+    'cyan',
+    'amber',
+    'emerald',
+    'violet',
+    'indigo',
+    'coral',
+    'teal',
+    'gold',
+    'silver',
+    'copper',
+    'bronze',
+    'ivory',
+    'jade',
+  ];
+
+  try {
+    const randomAdjective = adjectives[Math.floor(Math.random() * adjectives.length)];
+    const randomColor = colors[Math.floor(Math.random() * colors.length)];
+    const randomNoun = nouns[Math.floor(Math.random() * nouns.length)];
+
+    return `${randomAdjective}-${randomColor}-${randomNoun}`;
+  } catch {
+    // Fallback to unix timestamp if something goes wrong
+    return Date.now().toString();
+  }
+};