Add "lessons/patterns/setup-wizard-url-format-mismatch"

lessons%2Fpatterns%2Fsetup-wizard-url-format-mismatch.-.md

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+## Context
+
+When running `/cmdb-assistant:initial-setup` on a fresh server (banditlabs), all NetBox MCP tools failed with JSON parsing errors despite the API returning valid responses.
+
+- Command/tool: `dcim_list_devices`, `dcim_list_sites`
+- Error: `Invalid JSON response from NetBox: Expecting value: line 8 column 1 (char 7)`
+
+## Problem
+
+The `/initial-setup` command asked users for a "NetBox server URL" with example `https://netbox.company.com`, but the `NetBoxClient` expected the full API URL including `/api` suffix.
+
+**Root cause:** Inconsistency between setup wizard and code expectations:
+- Setup saved: `NETBOX_API_URL=https://netbox.hotserv.cloud`
+- Code expected: `NETBOX_API_URL=https://netbox.hotserv.cloud/api`
+
+The validation test in the setup wizard **incorrectly** appended `/api/` to the URL when testing, making it pass even though the saved config was wrong. This masked the bug during setup.
+
+## Solution
+
+1. Updated setup wizard example to show URL with `/api` suffix
+2. Added instruction to auto-append `/api` if user forgets
+3. Fixed validation test to use URL as-is (consistent with actual usage)
+
+**PR:** #132  
+**Files:** `plugins/cmdb-assistant/commands/initial-setup.md`
+
+## Prevention
+
+When writing setup wizards that save configuration:
+1. **Example values must match exact format expected by code**
+2. **Validation tests must use config exactly as saved** - don't transform it
+3. **Document URL format requirements explicitly** in prompts
+4. **Test fresh installations** on new machines, not just existing setups
+
+## Related
+
+- Issue: #126
+- PR: #132
+- Component: cmdb-assistant, NetBox MCP
+
+---
+**Tags:** cmdb-assistant, netbox, setup-wizard, configuration, url-format, validation, bug-fix