home: fix nav active-section at page bottom + exact progress bar; add blog tags to Writing

- Nav underline highlighted the wrong section at the bottom (the short last
  section never crossed the threshold) — force the last section when scrolled
  to the bottom so Contact lights up instead of Skills
- Scroll-progress bar: compute progress from scrollY/maxScroll so it spans a
  true 0→1 (Motion's default topped out ~0.89 at the bottom)
- Writing section: add blog tag chips linking to /blog/tags/<tag>/

src/pages/index.astro

@@ -8,13 +8,15 @@ import ProjectCard from "../components/ProjectCard.astro";
 import PostList from "../components/PostList.astro";
 import Contact from "../components/Contact.astro";
 import { skills } from "../data/skills";
-import { getPosts } from "../lib/blog";
+import { getPosts, allTags } from "../lib/blog";
 import { getCollection } from "astro:content";
 
 const featuredProjects = (await getCollection("projects", (p) => p.data.featured)).sort(
   (a, b) => a.data.order - b.data.order,
 );
-const recentPosts = (await getPosts()).slice(0, 3);
+const allPosts = await getPosts();
+const recentPosts = allPosts.slice(0, 3);
+const postTags = allTags(allPosts);
 ---
 
 <Layout path="/">
@@ -44,6 +46,14 @@ const recentPosts = (await getPosts()).slice(0, 3);
       Lessons from edge Kubernetes, GPUs, and running infrastructure like it matters —
       written up as I go.
     </p>
+    {postTags.length > 0 && (
+      <nav class="writing__tags" aria-label="Browse the blog by tag" data-reveal>
+        <span class="mono writing__tags-label">tags:</span>
+        {postTags.map((t) => (
+          <a class="tag" href={`/blog/tags/${t}/`}>{t}</a>
+        ))}
+      </nav>
+    )}
     <PostList posts={recentPosts} />
     <p class="projects__more" data-reveal>
       <a class="btn" href="/blog/">Read the blog →</a>
@@ -72,7 +82,18 @@ const recentPosts = (await getPosts()).slice(0, 3);
   }
   .writing__intro {
     max-width: 52ch;
-    margin-bottom: var(--space-5);
+    margin-bottom: var(--space-4);
     color: var(--text-dim);
   }
+  .writing__tags {
+    display: flex;
+    flex-wrap: wrap;
+    align-items: center;
+    gap: 0.5rem;
+    margin-bottom: var(--space-6);
+  }
+  .writing__tags-label {
+    font-size: var(--step--1);
+    color: var(--text-faint);
+  }
 </style>