Seed admin user from Config.json and fix config path case sensitivity for Linux

[devin-ai-integration]

Summary

Two changes:

1. Configurable seed admin credentials (ERPService.cs): The first admin user created during initial DB setup now reads credentials from Config.json under a SeedUser section, with fallback to the original defaults (erp@webvella.com / erp). To use custom credentials, add to Config.json:

   "SeedUser": {
     "FirstName": "Demo",
     "LastName": "Admin",
     "Email": "demo@cognition.ai",
     "Password": "password123"
   }

2. Linux case-sensitivity fix (Startup.cs, ErpMvcExtensions.cs): Changed config path from "config.json" to "Config.json" in both locations that load the config file, to match the actual filename on case-sensitive filesystems.

Review & Testing Checklist for Human

• Verify ErpSettings.Configuration is always initialized before InitializeSystemEntities() runs — if not, the config reads will throw a NullReferenceException
• Test with a fresh database (drop and recreate) both with and without the SeedUser section in Config.json — the fallback defaults should match the original behavior when the section is absent
• Seeding only runs on first DB initialization (version 0). Changing Config.json after initial setup will not update the existing user — confirm this is acceptable

Suggested test plan: Drop the database, start the app with a SeedUser section in Config.json, verify login works with the configured credentials. Then drop the database again, remove the SeedUser section, and verify login works with the original defaults (erp@webvella.com / erp).

Notes

• Config.json itself was not modified in this PR to avoid committing credentials to source control. The SeedUser section must be added manually to each deployment's config file.
• The config.json → Config.json case fix is a no-op on Windows (case-insensitive) but required for Linux/macOS.
• Tested end-to-end on a fresh database: login with demo@cognition.ai / password123 succeeded after adding the SeedUser section to the local Config.json.

Link to Devin session: https://app.devin.ai/sessions/4869a007cd7540c8944b1a59d5a3b15d
Requested by: @patrickbradley-cog

---

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.