iter emit-ir-staticlib: ail emit-ir --emit=staticlib (M1 fieldtest spec_gap#2)

Restores the Decision-5 IR-readability affordance for main-free
kernels: ail emit-ir gains --emit=staticlib, symmetric with
ail build, reusing the M1-audited Target::StaticLib path via a new
one-line lower_workspace_staticlib convenience. Zero-export guard
byte-identical to build_staticlib's. DESIGN.md widened (not
narrowed) + a pre-existing M1 synopsis omission corrected. 3 new
E2E tests; no fixture minted, no doc pin (E2E is the coverage).
Plan 03493c9.

crates/ailang-codegen/src/lib.rs

@@ -276,6 +276,18 @@ pub fn lower_workspace(ws: &Workspace) -> Result<String> {
     lower_workspace_inner(ws, AllocStrategy::Gc, Target::Executable)
 }
 
+/// Embedding-ABI M1 single-call entry point symmetric with
+/// [`lower_workspace`]: lowers a [`Workspace`] for the static-library
+/// target with the default `AllocStrategy::Gc`. This is what
+/// `ail emit-ir --emit=staticlib` calls so an author can read a
+/// `main`-free kernel's IR (the external `@<sym>` forwarders, no
+/// `@main`) — the Decision-5 IR-readability affordance for the
+/// artefact M1 introduced. Equivalent to
+/// `lower_workspace_staticlib_with_alloc(ws, AllocStrategy::Gc)`.
+pub fn lower_workspace_staticlib(ws: &Workspace) -> Result<String> {
+    lower_workspace_inner(ws, AllocStrategy::Gc, Target::StaticLib)
+}
+
 fn lower_workspace_inner(ws: &Workspace, alloc: AllocStrategy, target: Target) -> Result<String> {
     // Iter 16a: desugar every module before any lowering work runs.
     // The pass is idempotent and structurally identical to what