Move SX construction from Python to .sx defcomps (phases 0-4)

Eliminate Python s-expression string building across account, orders,
federation, and cart services. Visual rendering logic now lives entirely
in .sx defcomp components; Python files contain only data serialization,
header/layout wiring, and thin wrappers that call defcomps.

Phase 0: Shared DRY extraction — auth/orders header defcomps, format-decimal/
pluralize/escape/route-prefix primitives.
Phase 1: Account — dashboard, newsletters, login/device/check-email content.
Phase 2: Orders — order list, detail, filter, checkout return assembled defcomps.
Phase 3: Federation — social nav, post cards, timeline, search, actors,
notifications, compose, profile assembled defcomps.
Phase 4: Cart — overview, page cart items/calendar/tickets/summary, admin,
payments assembled defcomps; orders rendering reuses Phase 2 shared defcomps.

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

shared/sx/primitives.py

@@ -498,6 +498,15 @@ def prim_format_date(date_str: Any, fmt: str) -> str:
         return str(date_str) if date_str else ""
 
 
+@register_primitive("format-decimal")
+def prim_format_decimal(val: Any, places: Any = 2) -> str:
+    """``(format-decimal val places)`` → formatted decimal string."""
+    try:
+        return f"{float(val):.{int(places)}f}"
+    except (ValueError, TypeError):
+        return "0." + "0" * int(places)
+
+
 @register_primitive("parse-int")
 def prim_parse_int(val: Any, default: Any = 0) -> int | Any:
     """``(parse-int val default?)`` → int(val) with fallback."""
@@ -516,3 +525,34 @@ def prim_assert(condition: Any, message: str = "Assertion failed") -> bool:
     if not condition:
         raise RuntimeError(f"Assertion error: {message}")
     return True
+
+
+# ---------------------------------------------------------------------------
+# Text helpers
+# ---------------------------------------------------------------------------
+
+@register_primitive("pluralize")
+def prim_pluralize(count: Any, singular: str = "", plural: str = "s") -> str:
+    """``(pluralize count)`` → "s" if count != 1, else "".
+    ``(pluralize count "item" "items")`` → "item" or "items"."""
+    try:
+        n = int(count)
+    except (ValueError, TypeError):
+        n = 0
+    if singular or plural != "s":
+        return singular if n == 1 else plural
+    return "" if n == 1 else "s"
+
+
+@register_primitive("escape")
+def prim_escape(s: Any) -> str:
+    """``(escape val)`` → HTML-escaped string."""
+    from markupsafe import escape as _escape
+    return str(_escape(str(s) if s is not None and s is not NIL else ""))
+
+
+@register_primitive("route-prefix")
+def prim_route_prefix() -> str:
+    """``(route-prefix)`` → service URL prefix for dev/prod routing."""
+    from shared.utils import route_prefix
+    return route_prefix()