fix: Update actions/checkout to v6 and enhance CLAUDE.md generation prompt (#246)

Author: drobnikj

.github/prompts/claude-md-system-prompt.md

@@ -18,7 +18,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 
@@ -35,8 +35,58 @@ jobs:
           ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
           CLAUDE_CODE_NON_INTERACTIVE: "1"
         run: |
-          PROMPT=$(cat .github/prompts/claude-md-system-prompt.md)
-          claude --dangerously-skip-permissions --verbose -p "$PROMPT"
+          claude --dangerously-skip-permissions --verbose -p \
+            "You are an AI assistant responsible for keeping CLAUDE.md accurate and up to date in this repository.
+
+          ## Your Task
+
+          1. **Identify what changed.** Use git to find the files modified by the most recent merge or set of commits:
+             \`\`\`
+             git log --oneline -1
+             git diff HEAD~1 HEAD --name-only
+             \`\`\`
+             Read the changed files directly to understand the actual impact — do not rely solely on commit messages or diff output.
+
+          2. **Update CLAUDE.md surgically.**
+             - If \`CLAUDE.md\` does **not** exist: generate it from scratch (see structure below).
+             - If \`CLAUDE.md\` already exists: update **only the sections that are affected by the changes**. Leave unrelated sections untouched. Do not rewrite content that is still accurate.
+
+          3. **Write the result to \`CLAUDE.md\`** in the repository root.
+
+          ## CLAUDE.md Structure
+
+          Keep the file concise and useful as a reference for developers and AI agents. Cover only what is relevant for this repository — omit sections that do not apply.
+
+          \`\`\`
+          # CLAUDE.md
+
+          ## Project Purpose
+          What this repository is for and its high-level goals.
+
+          ## Repository Structure
+          Key directories and files with a brief description of each.
+
+          ## Technology Stack
+          Languages, frameworks, and major dependencies.
+
+          ## Build, Test & Run
+          Commands needed to install, build, test, and run the project locally.
+
+          ## Conventions
+          Code style, branching strategy, commit format, naming conventions, and other project-specific rules.
+
+          ## Key Notes for AI Assistants
+          Constraints, gotchas, or workflow-specific rules that an AI agent must know to avoid mistakes.
+          \`\`\`
+
+          ## Guidelines
+
+          - Be concise. Every line should earn its place.
+          - Do not add boilerplate, filler, or placeholder sections.
+          - Do not speculate about files you have not read — use the tools available to inspect actual content.
+          - When updating an existing CLAUDE.md, preserve sections that are still accurate. Only modify what the PR changes made outdated or incomplete.
+          - If the PR adds a new feature, dependency, or convention, add or extend the relevant section.
+          - If the PR removes something, delete the corresponding documentation."
 
       - name: Check for changes
         id: diff