chore: add installer for FlowState-TM Claude Code skill

.gitattributes

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+*.sh text eol=lf

scripts/install-claude-skill.sh

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+#!/usr/bin/env bash
+#
+# Install the FlowState-TM threat-model prompt as a user-level Claude Code skill.
+#
+# Reads .github/prompts/threat-model.prompt.md from the repo, strips the
+# VS Code prompt frontmatter, prepends Claude Code skill frontmatter, and
+# writes the result to ~/.claude/skills/flowstate-tm/SKILL.md.
+#
+# Usage:
+#   ./scripts/install-claude-skill.sh
+#
+# After running, restart Claude Code and invoke the skill with /flowstate-tm.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+SOURCE_FILE="$REPO_ROOT/.github/prompts/threat-model.prompt.md"
+SKILL_NAME="flowstate-tm"
+SKILL_DIR="$HOME/.claude/skills/$SKILL_NAME"
+SKILL_FILE="$SKILL_DIR/SKILL.md"
+
+if [ ! -f "$SOURCE_FILE" ]; then
+  echo "Error: source prompt not found at $SOURCE_FILE" >&2
+  echo "Run this script from a FlowState-TM checkout." >&2
+  exit 1
+fi
+
+mkdir -p "$SKILL_DIR"
+
+# Compose SKILL.md: new frontmatter + body of the source prompt (frontmatter stripped).
+# The awk filter prints every line after the second `---`, which removes the
+# original VS Code prompt frontmatter while leaving the markdown body intact.
+{
+  cat <<'EOF'
+---
+name: flowstate-tm
+description: Create a threat model using the FlowState-TM YAML format. Use when the user asks to generate, create, or update a threat model, security model, or STRIDE analysis, or asks for FlowState-TM YAML output.
+---
+EOF
+  awk 'BEGIN{p=0} /^---$/{c++; if(c==2){p=1; next}} p' "$SOURCE_FILE"
+} > "$SKILL_FILE"
+
+echo "Installed FlowState-TM skill to: $SKILL_FILE"
+echo "Restart Claude Code, then invoke with /$SKILL_NAME (or just ask for a threat model)."