feat(surveys): replace Formbricks with self-rendered PostHog API surveys

Formbricks CE turned out to gate person-based targeting (setUserId/attributes
→ 403 enterprise) — the exact flexibility surveys need. PostHog already holds
the person properties, so surveys move back there in API mode: posthog-js
evaluates eligibility (event triggers, targeting flags like
subscription_status=active, wait periods, per-distinct_id dedup) via
getActiveMatchingSurveys, and we render the popover ourselves — zero PostHog
branding, sase.tr dark-theme styling.

- lib/surveys.ts: display manager + capture payload builders that mirror
  posthog-js's own "survey shown/dismissed/sent" shapes exactly
  ($survey_response_<qid>, $set $survey_dismissed/<id>[/iter], seenSurvey_*,
  lastSeenSurveyDate) so the PostHog Surveys results UI works unchanged
- components/survey-popover.tsx: single_choice (+Diğer), open text, rating/NPS
- posthog.ts: capture/pageview/identify now schedule survey checks; register
  deploy_env (dev.sase.tr ships the key now → staging traffic is filterable)
- remove @formbricks/js, its CSP entries and build args

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/web/src/routes/__root.tsx

@@ -1,4 +1,5 @@
 import { InAppEscape } from "@/components/in-app-escape";
+import { SurveyPopover } from "@/components/survey-popover";
 import { useAuth } from "@/hooks/use-auth";
 import { api } from "@/lib/api-client";
 import { resetChatwootUser, setChatwootUser } from "@/lib/chatwoot";
@@ -156,6 +157,7 @@ function RootComponent() {
       </a>
       <InAppEscape />
       <Outlet />
+      <SurveyPopover />
       <Toaster position="top-center" />
     </>
   );