chore(web): add knip and remove unused npm dependencies

Drops highlight.js, lunr, autoprefixer, and @types/markdown-it —
all verified unreferenced (markdown-it ships its own types). Adds
knip.json configured for the templ/htmx architecture: main.ts and
reader/reader.ts entries, vitest tests as entry points, and an
ignore list for the ten modules whose exports are bound by templ
Alpine attributes — string bindings that static analysis cannot see.

package.json

@@ -18,9 +18,7 @@
     "chart.js": "^4.5.1",
     "dompurify": "^3.4.16",
     "fflate": "^0.8.3",
-    "highlight.js": "^11.11.1",
     "htmx.org": "^2.0.8",
-    "lunr": "^2.3.9",
     "markdown-it": "^15.0.2",
     "markdown-it-footnote": "^4.0.0",
     "turndown": "^7.2.4",
@@ -29,10 +27,9 @@
   "devDependencies": {
     "@tailwindcss/forms": "^0.5.11",
     "@tailwindcss/typography": "^0.5.19",
-    "@types/markdown-it": "^14.2.0",
     "@types/turndown": "^5.0.6",
-    "autoprefixer": "^10.4.27",
     "jsdom": "^30.1.3",
+    "knip": "^6.43.0",
     "playwright": "^1.64.1",
     "tailwindcss": "^3.4.19",
     "typescript": "^5.9.3",