chore: stop tracking web dist build artifacts

Add /web/dist to .gitignore, untrack the committed vite build output,
and update the embed.go comment to reflect that dist is generated by
the Makefile web target instead of being committed.

.gitignore

@@ -34,6 +34,7 @@
 /*.tf
 # frontend
 /web/node_modules
+/web/dist
 
 # agent working data (subagent artifacts, not project content)
 /.pi-subagents

web/dist/favicon.svg

@@ -1,15 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
-  <defs>
-    <linearGradient id="g" x1="0" y1="0" x2="32" y2="32" gradientUnits="userSpaceOnUse">
-      <stop offset="0%" stop-color="#0d9488"/>
-      <stop offset="100%" stop-color="#0f766e"/>
-    </linearGradient>
-  </defs>
-  <rect width="32" height="32" rx="7" fill="url(#g)"/>
-  <g fill="none" stroke="#f5f2e6" stroke-linecap="round" stroke-linejoin="round">
-    <circle cx="16" cy="24" r="3.5" fill="#f5f2e6" stroke="none"/>
-    <path d="M16 20.5 C16 15, 16 12, 16 8" stroke-width="3"/>
-    <path d="M16 12 L9.5 5.5" stroke-width="2.5"/>
-    <path d="M16 12 L22.5 5.5" stroke-width="2.5"/>
-  </g>
-</svg>

web/dist/index.html

@@ -1,15 +0,0 @@
-<!doctype html>
-<html lang="zh-CN">
-  <head>
-    <meta charset="UTF-8" />
-    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <meta name="color-scheme" content="light" />
-    <link rel="icon" href="/favicon.svg" type="image/svg+xml" />
-    <title>Sower Admin</title>
-    <script type="module" crossorigin src="/assets/index-C9pF9Fk-.js"></script>
-    <link rel="stylesheet" crossorigin href="/assets/index-BQCNGJsO.css">
-  </head>
-  <body>
-    <div id="app"></div>
-  </body>
-</html>

web/embed.go

@@ -1,6 +1,6 @@
 // Package web embeds the built admin console frontend into the binary.
-// The dist directory is generated by `bun run build` in this directory and
-// is committed so `go build` works without a frontend toolchain.
+// The dist directory is generated by `bun run build` in this directory
+// (see the Makefile `web` target, a prerequisite of the sower build).
 package web
 
 import (