ffi: drop static keyword on foreign-class methods; param type discriminates

`static name :: ...` was redundant — instance methods always declare
`self: *Self` as their first param by convention. The parser now derives
`is_static` from the first param's TYPE: if it's `*Self` the method is
an instance method; anything else (including no params at all) is a
class method. Removes a token from the surface, keeps the dispatch
behavior identical.

The receiver param's NAME doesn't matter — only its type. Calling the
first param `this`, `me`, `receiver`, etc. is fine as long as the type
is `*Self`. This mirrors how the rest of sx handles receiver dispatch.

Migration of every site that used the keyword:

- `library/modules/platform/android.sx` — `SurfaceView.new(ctx)`.
- `examples/ffi-jni-class-03-static.sx` — `Math.abs(n)`.
- `examples/ffi-jni-main-03-ctor.sx` — `SurfaceView.new(ctx)` in the
  `#jni_main` body.
- `examples/ffi-objc-dsl-05-static.sx` — NSObject's `.class()` /
  `.description()`.

164/164 example tests; chess clean on macOS / iOS sim / Android via
`tools/verify-step.sh`.

current/CHECKPOINT-FFI.md

@@ -501,6 +501,16 @@ plan's notional `::` — avoids a new postfix operator. Test:
 and `+description` class methods (NSObject is always available at
 module-load, unlike test classes created in main's body).
 
+Class-method declarations no longer need an explicit `static` keyword.
+The parser derives `is_static` from the first param's TYPE: if it's
+`*Self` the method is an instance method; anything else (including no
+params at all) is a class method. Surface examples now write
+`new :: (ctx: *JContext) -> *Self;` instead of
+`static new :: (...)`. The receiver param NAME doesn't matter — the
+type is the contract. Updated: `library/modules/platform/android.sx`,
+`examples/ffi-jni-class-03-static.sx`, `examples/ffi-jni-main-03-ctor.sx`,
+`examples/ffi-objc-dsl-05-static.sx`.
+
 Open work, in roughly the order they make sense:
 - **Phase 3 step 3.2** — `#selector("explicit:")` override + golden
   test for the default-mangling table. Escape hatch for selectors