ffi M2.2 (first pass): #property directive on foreign-class fields

Adds:
  field: T #property[(modifier, modifier, ...)];

inside #objc_class declarations. For FOREIGN classes (this slice),
'obj.field' and 'obj.field = x' lower as objc_msgSend dispatches —
no struct GEP, no per-field storage on the sx side. The receiver
is opaque and the Obj-C runtime owns the data.

Selector mangling (Apple convention):
  getter: <fieldName>            (e.g. 'count')
  setter: set<FieldName>:        (e.g. 'setBackgroundColor:')

So:
  view.backgroundColor          → [view backgroundColor]
  view.backgroundColor = red    → [view setBackgroundColor:red]

Plumbing:
- New token hash_property + lexer entry + LSP keyword classification.
- ForeignFieldDecl gains 'is_property' + 'property_modifiers' slice;
  the parser captures both. Modifiers are recorded verbatim (strong,
  weak, copy, readonly, getter("name"), ...) — semantic interpretation
  lands with M4.2 ARC wiring.
- lowerFieldAccess: lookupObjcPropertyOnPointer() detects the case
  before the auto-deref / struct-GEP path and dispatches via
  lowerObjcPropertyGetter (objc_msg_send).
- lowerAssignment: same check on the field_access LHS routes to
  lowerObjcPropertySetter (objc_msg_send with set<Field>:).
- inferExprType: 'obj.field' returns the property's declared type
  so chained access / coerced assignment work.

151-objc-property-foreign.sx round-trips:
  inst.tag        → [inst tag]       → reads g_probe_tag → 0
  inst.tag = 42   → [inst setTag:42] → writes g_probe_tag
  inst.tag = -7   → ditto
  Final: 0 -> 42 -> -7  (real Obj-C runtime dispatch).

DEFERRED for M2.2 (later passes):
- Sx-defined property IMPs (synthesized getter/setter trampolines
  reading/writing the state struct).
- Modifier-driven setter behavior: readonly (compile error on
  write), copy (deep-copy), weak (objc_storeWeak), strong/assign
  (Month 4.2 ARC ops).
- getter("name") / setter("name:") selector overrides.

181 example tests pass (+1). zig build test green.

src/ast.zig

@@ -561,6 +561,15 @@ pub const ForeignMethodDecl = struct {
 pub const ForeignFieldDecl = struct {
     name: []const u8,
     field_type: *Node, // type_expr node
+    /// True iff the declaration carries a `#property[(...)]` directive
+    /// (M2.2). For foreign classes, that means synthesize getter/setter
+    /// dispatch through `objc_msgSend`; for sx-defined classes it adds
+    /// runtime-introspectable property metadata + ARC-aware setter
+    /// emission (Month 4 wires the latter).
+    is_property: bool = false,
+    /// Comma-separated modifier names from `#property(strong, weak, ...)`.
+    /// Stored verbatim; semantic interpretation lands in M4.2.
+    property_modifiers: []const []const u8 = &.{},
 };
 
 pub const ForeignClassMember = union(enum) {