feat: make portfolio content crawlable + add SEO structured data

The entire portfolio rendered only on the PixiJS canvas, so crawlers saw a
near-empty body and the site ranked poorly for non-personalized searches. Fixes:

- NEW SeoContent.svelte: screen-reader/crawler-only (.sr-only) semantic HTML
  (h1 + bio + contact + Experience/Projects/Skills/Education), generated from
  data.ts (single source of truth, reuses aggregateSkills). Prerenders into
  build/index.html — verified it now contains the job/project/education text
  that was previously canvas-only. Also a big screen-reader accessibility win.
- JSON-LD schema.org Person in +layout (name, jobTitle, alumniOf, knowsAbout,
  sameAs LinkedIn/GitHub) — strong entity signal for name searches.
- Canonical URL; static/sitemap.xml + robots.txt Sitemap reference.
- Keyword-tuned <title>, description, og/twitter titles (name + role + stack).
- Demoted the transient welcome <h1> to a <div> so SeoContent's <h1> is the
  single canonical heading. Bumped SW cache to v2.

.sr-only utility added to app.css. check/lint/test/build clean; verified no
visual regression and no runtime exceptions (background + canvas unchanged).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/components/SeoContent.svelte

@@ -0,0 +1,122 @@
+<script lang="ts">
+	// Screen-reader / crawler-only rendition of the portfolio.
+	//
+	// The interactive tree lives entirely on a PixiJS canvas, which search
+	// engines and assistive tech can't read. This component renders the same
+	// content (sourced from data.ts — the single source of truth) as real,
+	// prerendered semantic HTML, visually hidden via the global `.sr-only` class.
+	import {
+		treeNodes,
+		type ExperienceNode,
+		type ProjectNode,
+		type EducationNode,
+		type OriginNode
+	} from '$lib/data';
+	import { aggregateSkills, BRANCH_IDS } from '$lib/utils/stats';
+
+	const origin = treeNodes.find((n): n is OriginNode => n.category === 'origin');
+
+	// Leaf nodes only — container/branch nodes lack these category fields.
+	const jobs = treeNodes.filter(
+		(n): n is ExperienceNode => n.category === 'experience' && !!n.company
+	);
+	const projects = treeNodes.filter(
+		(n): n is ProjectNode => n.category === 'projects' && !!n.techStack?.length
+	);
+	const education = treeNodes.filter(
+		(n): n is EducationNode => n.category === 'education' && !!n.institution
+	);
+
+	// Newest experience first (reverse-chronological, résumé convention).
+	const jobsNewestFirst = [...jobs].reverse();
+
+	const skillsByBranch = aggregateSkills();
+</script>
+
+{#if origin}
+	<section class="sr-only" aria-label="Portfolio (text version)">
+		<h1>{origin.fullName} — {origin.jobTitle}</h1>
+		{#if origin.aboutMe}<p>{origin.aboutMe}</p>{/if}
+		{#if origin.location}<p>Location: {origin.location}</p>{/if}
+
+		<nav aria-label="Contact and profiles">
+			<ul>
+				{#if origin.email}<li><a href="mailto:{origin.email}">Email: {origin.email}</a></li>{/if}
+				{#if origin.linkedIn}<li><a href={origin.linkedIn}>LinkedIn</a></li>{/if}
+				{#if origin.github}<li><a href={origin.github}>GitHub</a></li>{/if}
+				{#if origin.website}<li><a href={origin.website}>Website</a></li>{/if}
+				{#if origin.resumeUrl}<li><a href={origin.resumeUrl}>Résumé (PDF)</a></li>{/if}
+			</ul>
+		</nav>
+
+		<section aria-label="Work experience">
+			<h2>Work Experience</h2>
+			{#each jobsNewestFirst as job (job.id)}
+				<article>
+					<h3>{job.jobTitle} — {job.company}</h3>
+					{#if job.startDate}<p>{job.startDate} – {job.endDate || 'Present'}</p>{/if}
+					{#if job.highlights?.length}
+						<ul>
+							{#each job.highlights as highlight (highlight)}
+								<li>{highlight}</li>
+							{/each}
+						</ul>
+					{/if}
+				</article>
+			{/each}
+		</section>
+
+		<section aria-label="Projects">
+			<h2>Projects</h2>
+			{#each projects as project (project.id)}
+				<article>
+					<h3>{project.label}</h3>
+					<p>{project.description}</p>
+					{#if project.techStack?.length}
+						<p>Tech: {project.techStack.join(', ')}</p>
+					{/if}
+					<ul>
+						{#if project.projectUrl}<li><a href={project.projectUrl}>Live site</a></li>{/if}
+						{#if project.repoUrl}<li><a href={project.repoUrl}>Source code</a></li>{/if}
+						{#if project.pypiUrl}<li><a href={project.pypiUrl}>PyPI package</a></li>{/if}
+						{#if project.npmUrl}<li><a href={project.npmUrl}>npm package</a></li>{/if}
+					</ul>
+				</article>
+			{/each}
+		</section>
+
+		<section aria-label="Technical skills">
+			<h2>Technical Skills</h2>
+			{#each BRANCH_IDS as branchId (branchId)}
+				{@const branch = skillsByBranch[branchId]}
+				{#if branch && branch.skills.length}
+					<h3>{branch.label}</h3>
+					<ul>
+						{#each branch.skills as skill (skill.id)}
+							<li>
+								{skill.label}{#if skill.proficiency}
+									({skill.proficiency}{#if skill.yearsOfExperience}, {skill.yearsOfExperience} years{/if})
+								{/if}
+							</li>
+						{/each}
+					</ul>
+				{/if}
+			{/each}
+		</section>
+
+		<section aria-label="Education">
+			<h2>Education</h2>
+			{#each education as edu (edu.id)}
+				<article>
+					<h3>
+						{edu.degree}{#if edu.field}
+							in {edu.field}{/if}
+					</h3>
+					<p>
+						{edu.institution}{#if edu.graduationYear}, {edu.graduationYear}{/if}
+					</p>
+				</article>
+			{/each}
+		</section>
+	</section>
+{/if}