Add chat-first onboarding and intelligent context-based paywall

Replaces the hardcoded message limit with a model-driven paywall and
removes registration before the first question:

- Onboarding: the app opens directly into the chat. Dynamic conversation
  starters are served by GET /suggestions (services/api/suggestions.json),
  updatable with a deploy — no app release needed. Guests chat via
  POST /guest/chat, identified by an app-generated device id; sign-in
  moves to the paywall, where a purchase must attach to an account.
- Free experience: the model runs in discovery mode — follow-up
  questions, pattern identification, visible understanding — building an
  analysis without delivering the full solution.
- Intelligent paywall: the model returns structured output (reply +
  analysis_ready). Only when the problem is described, the information is
  sufficient and an action plan is ready does it write a calm transition
  and pause the conversation. Manufactured urgency, emotional pressure,
  fake readiness and mid-answer stops are explicitly forbidden.
- Premium: on unlock the app resends the transcript and the backend
  immediately delivers the full analysis, strategies and exercises, then
  the dialogue continues without restriction.
- The old FREE_MESSAGE_LIMIT becomes MESSAGE_CAP (default 200/30 days),
  kept purely as an abuse backstop — it is not the paywall.
- WelcomeScreen removed; the app is now two views (Chat, Paywall).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0118DaxZR36RpnY524vRqx3z

services/api/suggestions.json

@@ -0,0 +1,14 @@
+{
+  "suggestions": [
+    "I need support before a difficult conversation.",
+    "Help me prepare for a salary negotiation.",
+    "I'm going on a first date.",
+    "Why do I get stuck in the same conflicts?",
+    "Help me understand my reactions.",
+    "How do I set clearer boundaries?",
+    "I want to become a better communicator.",
+    "Help me prepare for a job interview.",
+    "How do I build better self-confidence?",
+    "Help me make a difficult decision."
+  ]
+}