docs(layout): pin the legal-page narrow-column convention in code comments

The privacy + about pages constrain their main column to `max-w-3xl`
(768 px) while the rest of the app uses `max-w-screen-xl` (1280 px).
That's a deliberate readability choice -- long-form legal text is
easier to read at 70-80 chars per line -- but the convention wasn't
documented inline, so a future contributor could see the deviation
from the shell width as a stale token and "fix" it.

Inline rationale comment on both `<main>` blocks per the audit
finding §3.4. No layout change.

src/app/about/page.tsx

@@ -81,6 +81,12 @@ export default function AboutPage() {
         </div>
       </header>
 
+      {/*
+        v1.4.33 IW9 — `max-w-3xl` is intentional (same rationale as
+        `/privacy`): long-form column reads better around 70-80
+        chars per line. The dashboard / settings / admin shells use
+        `max-w-screen-xl` (1280 px); legal pages stay at 768 px.
+      */}
       <main
         id="main-content"
         className="mx-auto max-w-3xl space-y-10 px-4 py-8 md:px-6 md:py-12"

src/app/privacy/page.tsx

@@ -124,6 +124,13 @@ export default function PrivacyPage() {
         </div>
       </header>
 
+      {/*
+        v1.4.33 IW9 — `max-w-3xl` (768 px) is intentional, not a stale
+        token. The legal/long-form column reads better at 70-80 chars
+        per line; widening to the app shell's `max-w-screen-xl` would
+        push line lengths to ~120 chars on a 1440 px laptop and degrade
+        legibility. The same exception applies to `/about`.
+      */}
       <main
         id="main-content"
         className="mx-auto max-w-3xl space-y-10 px-4 py-8 md:px-6 md:py-12"