feat(brand): add dbopt logo, favicon, and wordmark lockup

A Neelkanth-blue mark: a database cylinder that subtly reads as a Shivling
(domed top + yoni-spout base), with three tripundra lines and a red tilak
centred on the middle line. Vector SVG, render-verified from 96px to 16px.

- web/public/logo.svg        primary mark
- web/public/favicon.svg     same mark on a dark tile (wired into index.html)
- web/public/logo-lockup.svg mark + lowercase "dbopt" wordmark

Author: sqlopt

web/index.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <meta name="color-scheme" content="dark" />
+    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
     <title>dbopt · SQL Server observatory</title>
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />