ui: keep the board visible in light mode + bust diagram cache

Light mode: revert the heavy white-out scrim back to a moderate wash so the
board stays visible, and earn legibility with a soft light text-halo behind
running text instead (invisible on the solid cards, only works over the image).
Pairs with the darker light-mode text tokens.

Also append ?v=2 to every /diagrams/*.svg reference so the recoloured diagrams
bypass Cloudflare's 4h edge cache and show immediately (the SVG URLs aren't
content-hashed like the CSS bundle).

src/content/blog/workload-least-privilege.md

@@ -14,7 +14,7 @@ a DNS sinkhole, a search proxy — the answer is no. Never. Not once.
 So every one of those pods is holding a key to a door it never opens. That's not least privilege. That's a
 standing credential waiting to be stolen.
 
-![Workload least privilege — each pod gets its own ServiceAccount with no API token, runs non-root with capabilities dropped, inside a namespace whose Pod Security level is pinned; the cluster API it never calls stays out of reach](/diagrams/workload-least-privilege.svg)
+![Workload least privilege — each pod gets its own ServiceAccount with no API token, runs non-root with capabilities dropped, inside a namespace whose Pod Security level is pinned; the cluster API it never calls stays out of reach](/diagrams/workload-least-privilege.svg?v=2)
 
 ## Identity first, RBAC second