Remove unused env var and reorder rewrites (#1069)

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## Summary
The PostHog reverse-proxy catch-all rewrite (/ingest/:path*) was ordered
before the more specific /ingest/decide and /ingest/static/:path*
rewrites, causing it to swallow those routes. This moves the catch-all
to after the specific rewrites so they match first.

Also removes the unused NEXT_PUBLIC_POSTHOG_HOST env var from .env.

## Verification
- Confirmed rewrite order in next.config.mjs places
/ingest/static/:path* and /ingest/decide before the catch-all
/ingest/:path*
  - No build errors introduced

## Reviewer Notes
Next.js rewrites are evaluated top-down and first-match wins. The
catch-all was previously shadowing the specific routes. A comment is
added inline to prevent future reordering.

Author: evanjacobson

.env

@@ -4,7 +4,6 @@ DEBUG_AUTH=
 STRIPE_TOP_UP_PRICE_ID=price_1RjLOnJ7A6SsvrfSlQLRoy7x
 
 # posthog - not secret, not really useful for most dev, but _not_ loading it would increase the diff with prod.
-NEXT_PUBLIC_POSTHOG_HOST="https://us.i.posthog.com"
 NEXT_PUBLIC_POSTHOG_KEY=phc_GK2Pxl0HPj5ZPfwhLRjXrtdz8eD7e9MKnXiFrOqnB6z
 
 # Database

next.config.mjs

@@ -50,18 +50,20 @@ const nextConfig = {
           source: '/config.json',
           destination: 'https://opencode.ai/config.json',
         },
+        // PostHog reverse proxy rewrites — specific routes MUST come before the catch-all
         {
           source: '/ingest/static/:path*',
           destination: 'https://us-assets.i.posthog.com/static/:path*',
         },
-        {
-          source: '/ingest/:path*',
-          destination: 'https://us.i.posthog.com/:path*',
-        },
         {
           source: '/ingest/decide',
           destination: 'https://us.i.posthog.com/decide',
         },
+        // Catch-all must be last — otherwise it swallows /decide and /static
+        {
+          source: '/ingest/:path*',
+          destination: 'https://us.i.posthog.com/:path*',
+        },
         {
           source: '/.well-known/appspecific/com.chrome.devtools.json',
           destination: '/api/chrome-devtools',