Fix: Reset invalid accounts on startup and improve project discovery logging

Fixes #33 - Accounts marked as invalid were permanently stuck because
the isInvalid flag was persisted to disk but never reset on startup.

Changes:
- Reset isInvalid flag for all accounts on server startup, giving them
  a fresh chance to refresh their OAuth tokens
- Add logging for project discovery failures (was silently failing)
- Add success logging when project is discovered
- Add warning message when falling back to default project

Bug introduced in 01cda83 (2025-12-25) when isInvalid persistence was
added without corresponding reset logic on load.

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

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

src/account-manager/storage.js

@@ -28,7 +28,10 @@ export async function loadAccounts(configPath = ACCOUNT_CONFIG_PATH) {
             ...acc,
             isRateLimited: acc.isRateLimited || false,
             rateLimitResetTime: acc.rateLimitResetTime || null,
-            lastUsed: acc.lastUsed || null
+            lastUsed: acc.lastUsed || null,
+            // Reset invalid flag on startup - give accounts a fresh chance to refresh
+            isInvalid: false,
+            invalidReason: null
         }));
 
         const settings = config.settings || {};