atomics: close out Stream A (feature-complete)

Final whole-stream adversarial review came back CLEAN (no CRITICAL/MEDIUM/LOW).
Close the one informational gap it noted: extend examples/1703 with a #run
comptime swap so swap's comptime VM arm is locked (742, matches runtime) — every
op now has comptime↔runtime corpus coverage.

Docs: PLAN-ATOMICS.md status banner (COMPLETE); PLAN-POST-METATYPE.md Stream A
marked done (unblocks B2-channels + C-parallel); readme.md gains a user-facing
Atomics section. Suite green (721/0).

current/PLAN-POST-METATYPE.md

@@ -19,7 +19,7 @@ JIT/FFI cluster comes after. New corpus categories: `17xx` atomics, `18xx` concu
 
 | # | Stream | Roadmap steps | Depends on | Notes |
 |---|--------|---------------|-----------|-------|
-| **A** | Atomics | N1 (1) | — | independent foundation; gates B-parallel + channels |
+| **A** | Atomics | N1 (1) | — | ✅ **DONE** — `PLAN-ATOMICS.md`. load/store/RMW/CAS/swap/fence; comptime value params landed alongside. Gates B2-channels + C-parallel |
 | **B** | Async runtime | 4–12 | metatype, A (for channels) | the bulk; likely splits into B1 (runtime) + B2 (channels/cancel/stdlib) when carved |
 | **C** | Parallel schedulers | 13–14 | A, B | N×(M:1) → M:N |
 | **D** | Comptime JIT/FFI | 15–18 | — (independent of async) | S1 → C1 → C2 → C3 |
@@ -31,7 +31,7 @@ earlier if FFI/`#compiler`-collapse becomes a priority).
 
 ---
 
-## Stream A — ATOMICS (N1)  ·  `PLAN-ATOMICS.md` when carved
+## Stream A — ATOMICS (N1)  ·  ✅ **COMPLETE** — see [PLAN-ATOMICS.md](PLAN-ATOMICS.md)
 
 **Goal:** LLVM atomic codegen — the net-new emit primitive. Surface = `Atomic($T)`
 wrapper + `Ordering` enum (locked, design §4.6). **Grounding correction: this is 100%