Phase 6: Replace render_template() with s-expression rendering in all GET routes

Migrate ~52 GET route handlers across all 7 services from Jinja
render_template() to s-expression component rendering. Each service
gets a sexp_components.py with page/oob/cards render functions.

- Add per-service sexp_components.py (account, blog, cart, events,
  federation, market, orders) with full page, OOB, and pagination
  card rendering
- Add shared/sexp/helpers.py with call_url, root_header_html,
  full_page, oob_page utilities
- Update all GET routes to use get_template_context() + render fns
- Fix get_template_context() to inject Jinja globals (URL helpers)
- Add qs_filter to base_context for sexp filter URL building
- Mount sexp_components.py in docker-compose.dev.yml for all services
- Import sexp_components in app.py for Hypercorn --reload watching
- Fix route_prefix import (shared.utils not shared.infrastructure.urls)
- Fix federation choose-username missing actor in context
- Fix market page_markets missing post in context

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

federation/bp/identity/routes.py

@@ -39,7 +39,11 @@ def register(url_prefix="/identity"):
         if actor:
             return redirect(url_for("activitypub.actor_profile", username=actor.preferred_username))
 
-        return await render_template("federation/choose_username.html")
+        from shared.sexp.page import get_template_context
+        from sexp_components import render_choose_username_page
+        ctx = await get_template_context()
+        ctx["actor"] = actor
+        return await render_choose_username_page(ctx)
 
     @bp.post("/choose-username")
     async def choose_username():