refactor: rename third-party JS libs folder from vendor to lib

Rename static/shared/js/vendor/ to static/shared/js/lib/ to avoid
confusion with the app's "vendor" (seller) dashboard code in
static/vendor/js/.

- Rename directory: vendor/ → lib/
- Update all template references to use new path
- Update CDN fallback documentation
- Fix .gitignore to use /lib/ (root only) instead of lib/ (everywhere)

Third-party libraries:
- alpine.min.js
- chart.umd.min.js
- flatpickr.min.js
- quill.js
- tom-select.complete.min.js

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/development/troubleshooting.md

@@ -505,13 +505,13 @@ All frontends use CDN with local fallback. Check that local copies exist:
 ```bash
 # From project root
 ls -lh static/shared/css/tailwind.min.css
-ls -lh static/shared/js/vendor/alpine.min.js
+ls -lh static/shared/js/lib/alpine.min.js
 ```
 
 **Expected output:**
 ```
 -rw-r--r-- 1 user user 2.9M static/shared/css/tailwind.min.css
--rw-r--r-- 1 user user  44K static/shared/js/vendor/alpine.min.js
+-rw-r--r-- 1 user user  44K static/shared/js/lib/alpine.min.js
 ```
 
 **If files are missing:**
@@ -569,7 +569,7 @@ app.mount("/static", StaticFiles(directory="static"), name="static")
 ```bash
 # With app running, test directly:
 curl http://localhost:8000/static/shared/css/tailwind.min.css | head -n 5
-curl http://localhost:8000/static/shared/js/vendor/alpine.min.js | head -n 5
+curl http://localhost:8000/static/shared/js/lib/alpine.min.js | head -n 5
 ```
 
 ### Solution 5: File Permissions
@@ -579,7 +579,7 @@ If files exist but return 403 Forbidden:
 ```bash
 # Fix permissions
 chmod 644 static/shared/css/tailwind.min.css
-chmod 644 static/shared/js/vendor/alpine.min.js
+chmod 644 static/shared/js/lib/alpine.min.js
 chmod 755 static/shared/css
 chmod 755 static/shared/js/vendor
 ```