Remove company header and add Why Piha? section (#6)

## Summary

- Drop the company_site nav (logo, Home, Web Design, Contact) from the shortener chrome — that header belongs on aimloperations.com, not `piha.lc`
- Add a **Why Piha?** section: Quenya (Tolkien High Elvish) *pia* / *pitya* / *pincë* / *picina* means little / small; a short link is a little path
- Footer and Request access / Contact CTAs stay

Closes #5.

## Test plan

- [ ] `cd site && uv run python manage.py test`
- [ ] `GET /` has no top header; Why Piha? is on the page
- [ ] Request access / Contact still go to aimloperations.com/contact
- [ ] Debug mint page still works without the nav
- [ ] `GET /<code>` still 302

Reviewed-on: #6

site/links/tests.py

@@ -262,8 +262,11 @@ class RedirectTests(TestCase):
         self.assertEqual(response.status_code, 200)
         self.assertContains(response, "piha.lc")
         self.assertContains(response, "Request access")
+        self.assertContains(response, "Why Piha?")
+        self.assertContains(response, "Quenya")
         self.assertContains(response, "aimloperations.com")
         self.assertContains(response, "Contact")
+        self.assertNotContains(response, "<nav")
         self.assertNotContains(response, "Create a short link")
 
     def test_click_row_and_count(self):