chore(dev): Add Flox for local environment setup

.envrc

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+if [ -z "${FLOX_VERSION}" ]; then # Don't activate if already activated
+    flox activate
+fi

.flox/.gitignore

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+run/
+cache/
+lib/
+log/

.flox/env.json

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+{
+    "name": "posthog",
+    "version": 1
+}

.flox/env/direnv-setup.sh

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+#!/bin/bash
+
+if ! command -v direnv &> /dev/null; then
+    # Install direnv based on platform
+    if command -v brew &> /dev/null; then
+        echo "🔄 Installing direnv using 'brew install direnv'..."
+        HOMEBREW_NO_ENV_HINTS=1 brew install -q direnv
+    elif command -v apt &> /dev/null; then
+        echo "🔄 Installing direnv using 'apt install direnv'..."
+        sudo apt update && sudo apt install -yq direnv
+    elif command -v dnf &> /dev/null; then
+        echo "🔄 Installing direnv using 'dnf install direnv'..."
+        sudo dnf install -yq direnv
+    else
+        echo "🔄 Installing direnv using 'curl -sfL https://direnv.net/install.sh | bash'"
+        curl -sfL https://direnv.net/install.sh | bash
+    fi
+    echo "✅ Installed direnv"
+else
+    echo "⏩ direnv already installed"
+fi
+
+# Determine shell and config file
+shell_name=$(basename "$SHELL")
+case "$shell_name" in
+    "bash")
+    config_file="$HOME/.bashrc"
+    hook_command='eval "$(direnv hook bash)"'
+    ;;
+    "zsh")
+    config_file="$HOME/.zshrc"
+    hook_command='eval "$(direnv hook zsh)"'
+    ;;
+    "fish")
+    config_file="$HOME/.config/fish/config.fish"
+    hook_command='direnv hook fish | source'
+    mkdir -p "$(dirname "$config_file")"
+    ;;
+    "tcsh")
+    config_file="$HOME/.cshrc"
+    hook_command='eval `direnv hook tcsh`'
+    ;;
+    *)
+    echo "Unsupported shell: $shell_name"
+    return 1
+    ;;
+esac
+
+echo "🐚 Configuring your default shell, $SHELL, for direnv"
+
+# Add hook to shell config if not already present
+if ! grep -q "direnv hook" "$config_file" 2>/dev/null; then
+    echo -e "\n# Initialize direnv - added by PostHog's Flox activation hook (../posthog/.flox/env/manifest.toml)\n$hook_command" >> "$config_file"
+    echo "✅ Injected direnv hook into $config_file"
+else
+    echo "⏩ direnv hook already present in $config_file"
+fi
+
+# Add hook to shell config if not already present
+if ! grep -q "warn_timeout" "$HOME/.config/direnv/direnv.toml" 2>/dev/null; then
+    echo "[global]\nwarn_timeout = 0 # Ignore timeout from this issue: https://github.com/direnv/direnv/issues/1065 - added by PostHog's Flox activation hook (../posthog/.flox/env/manifest.toml)" >> "$HOME/.config/direnv/direnv.toml"
+    echo "✅ Configured ~/.config/direnv/direnv.toml"
+else
+    echo "⏩ ~/.config/direnv/direnv.toml already configured"
+fi
+
+echo "💫 direnv is now active"
+
+# Allow this directory's .envrc to be loaded
+direnv allow