fix: add ADMIN_PUBLIC_KEYS to .env.example (fixes #4)

[presidojay1]

Summary

Fixes #4 - Adds missing ADMIN_PUBLIC_KEYS environment variable to .env.example with comprehensive documentation and startup warning.

Problem

Fresh installs of SentientFi experience mysterious 503 errors on admin routes because ADMIN_PUBLIC_KEYS is not documented in .env.example. Developers have no way to know:

• That this variable exists
• What format it requires
• Which routes require it
• Why admin endpoints return 503

Changes Made

1. Updated backend/.env.example

• ✅ Added ADMIN_PUBLIC_KEYS with clear documentation
• ✅ Explained which admin routes are protected
• ✅ Provided example format (comma-separated public keys)
• ✅ Documented consequences of not setting it

2. Updated backend/src/index.ts

• ✅ Added startup warning when ADMIN_PUBLIC_KEYS is not set
• ✅ Warning lists affected admin routes clearly
• ✅ Developers are immediately informed at startup

Admin Routes Protected

The following routes require ADMIN_PUBLIC_KEYS configuration:

• POST /api/auto-rebalancer/start
• POST /api/auto-rebalancer/stop
• POST /api/auto-rebalancer/force-check
• GET /api/auto-rebalancer/history
• POST /api/rebalance/history/sync-onchain

Testing

Before Fix

# Fresh install - no indication ADMIN_PUBLIC_KEYS is needed
npm run dev
curl -X POST http://localhost:3001/api/auto-rebalancer/start
# Returns: 503 (no explanation)

After Fix

# Fresh install - clear warning at startup
npm run dev
# Console shows: ⚠️  ADMIN_PUBLIC_KEYS is not set — admin routes will return 503

# Developer knows to add ADMIN_PUBLIC_KEYS to .env
ADMIN_PUBLIC_KEYS=GADMIN123... npm run dev
# Admin routes now work ✅

Closes #4

Impact

• ✅ No more mysterious 503 errors on fresh installs
• ✅ Clear path to enabling admin features
• ✅ Improved developer experience
• ✅ Better onboarding for new contributors

Files Changed

• backend/.env.example - Added ADMIN_PUBLIC_KEYS documentation
• backend/src/index.ts - Added startup warning

Breaking Changes

None - All changes are backward compatible and purely additive.

Checklist

• Issue bug: ADMIN_PUBLIC_KEYS missing from .env.example — admin routes return 503 on fresh installs #4 fixed
• Changes tested locally
• No breaking changes
• Documentation added
• Commit follows conventional format