Rebuild the site as a terminal-style agent on Astro

Replace the single Gatsby page with a dark, terminal-style agent that answers
questions about Dennis's work from one curated knowledge base. There is no
model and no network call, so answers cannot be invented. A plain "Classic
view" and an optional light theme sit one click away.

Site
- Terminal UI (React island): typed answers, tool-call lines, slash commands,
  autocomplete, history, deep links, a short /oncall game
- Content focused on what recruiters scan for; personal and employer-internal
  details are left out
- No profile photo anywhere, including the new link-preview card and icons
- Corrected facts from the old page (dates, titles, tenses, skill tiers)

Tooling
- Migrate Gatsby 5 to Astro 7 (Node 22.23+); builds in about 1 second
- Self-host fonts, so visitors make no request to third parties
- Link-preview card, favicon set, web manifest and a service-worker clean-up
  for returning visitors
- Deploy workflow builds with npm ci on Node 22 and uploads dist/
- Track package-lock.json

Quality
- Tests for routing and for markup injection from visitor input
- A content guard scans every reachable answer; the list of things that must
  never be published lives in a git-ignored local file

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

test/private-banned.mjs

@@ -0,0 +1,27 @@
+// Loads the git-ignored list of specifics that must never reach the site. Without the file
+// (a fresh clone, CI) the generic rules in the tests still run, and a note says what was skipped.
+
+import { readFileSync } from 'node:fs'
+
+const FILE = new URL('./banned.private.json', import.meta.url)
+
+let loaded = { patterns: [], questions: [], answerPattern: null }
+let present = false
+try {
+  loaded = { ...loaded, ...JSON.parse(readFileSync(FILE, 'utf8')) }
+  present = true
+} catch (e) {
+  console.warn(
+    'note: test/banned.private.json not found; private content checks skipped'
+  )
+}
+
+export const privatePresent = present
+export const privatePatterns = loaded.patterns.map(([source, why]) => [
+  new RegExp(source, 'i'),
+  why,
+])
+export const privateQuestions = loaded.questions
+export const privateAnswerPattern = loaded.answerPattern
+  ? new RegExp(loaded.answerPattern, 'i')
+  : null