feat: Add simplified quickstart guide for easier onboarding (#157)

* feat: Add simplified quickstart guide and minimal env configuration

- Add QUICKSTART.md with streamlined setup instructions
- Create .env.quickstart with only essential configuration variables
- Focus on getting users running quickly with Cloudflare Tunnel
- Add Discord and documentation badges for community support
- Update .gitignore to include .env.quickstart

The quickstart guide provides a clear path from zero to running webhook
in approximately 15 minutes, using Claude Max subscription authentication
via the interactive setup script.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: Exclude .env.quickstart from credential audit false positives

The .env.quickstart file is a template with placeholder values and should not be flagged as a security issue during credential audits.

* fix: Update Discord server ID from placeholder to actual ID

Replace the placeholder Discord server ID (1234567890) with the actual
server ID (1313320949214814228) in the Discord badge. This fixes the
issue identified in PR #157 review where the badge was showing a
placeholder value.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: Update Discord server ID and add missing EOF newline

- Update Discord server ID to correct value (1377708770209304676)
- Add missing newline at end of .env.quickstart for POSIX compliance
- Addresses PR #157 review comments

---------

Co-authored-by: Claude <noreply@anthropic.com>

scripts/security/credential-audit.sh

@@ -32,8 +32,8 @@ report_success() {
 
 # 1. Check for .env files that shouldn't be committed
 echo "🔍 Checking for exposed .env files..."
-if find . -name ".env*" -not -path "./node_modules/*" -not -name ".env.example" -not -name ".env.template" | grep -q .; then
-    find . -name ".env*" -not -path "./node_modules/*" -not -name ".env.example" -not -name ".env.template" | while read file; do
+if find . -name ".env*" -not -path "./node_modules/*" -not -name ".env.example" -not -name ".env.template" -not -name ".env.quickstart" | grep -q .; then
+    find . -name ".env*" -not -path "./node_modules/*" -not -name ".env.example" -not -name ".env.template" -not -name ".env.quickstart" | while read file; do
         report_issue "Found .env file that may contain secrets: $file"
     done
 else