iter design-md-rolesplit.1 (DONE 9/9): DESIGN.md -> design/ ledger role-split

The 3020-line docs/DESIGN.md is replaced by the design/ ledger:
design/INDEX.md (sole addressable spine, typed Contracts+Models tables,
polymorphic links — prose file OR authoritative source //!), 14
design/contracts/*.md test-linked invariants + 3 source-link-only
contracts (mangling/env-construction/qualified-xref, no prose file —
code is SoT), 5 design/models/*.md whitepapers, and
docs/journals/2026-05-19-design-decision-records.md (the
relitigation-guard archive — every why/rejected/does-not-do/rollback/
empirical ### moved out at ###-granularity). Clean cut: git rm
docs/DESIGN.md, no stub.

RED-first crates/ailang-core/tests/design_index_pin.rs — the 4-clause
anti-regrowth spine (DESIGN.md-gone / every-INDEX-link-resolves /
every-contract-names-a-resolvable-ratifier /
contracts-carry-no-decision-record-prose) — demonstrably RED before,
GREEN after. Build-atomic by task ordering: design_schema_drift.rs's
include_str! (the only compile-time consumer) retargeted to
design/contracts/data-model.md BEFORE the deletion; its
## Data model/## Pipeline slicer dropped (a simplification the split
enables). 2 NoInstance diagnostics + 2 lockstep E2Es retargeted to
design/contracts/{float-semantics,typeclasses}.md. ~12 agent reading
lists + 5 SKILL bodies + CLAUDE.md + skills/README.md + ~25
code/C/.ail/spec comment xrefs retargeted; OQ7 dangling 'Iter 13b'
cite deleted (no forward target — a pointer would be fiction).
honesty-rule.md rewritten so the rule names the new home
(rationale->journals), resolving the recon-found internal
contradiction; the two docs_honesty_pin.rs:70,72 pinned phrases kept
verbatim+contiguous.

Boss-verified independently: cargo test --workspace 646 passed /
0 failed; design_index_pin 4/4; acceptance grep CLEAN of live
DESIGN.md refs (residuals = only the spec-mandated clause-4
deletion-enforcer). 2 DONE_WITH_CONCERNS routed to the mandatory
milestone-close audit: (a) str-abi.md:23 '(iter str-concat,
2026-05-13)' provenance stamp trips advisory architect_sweeps Sweep-1
— Boss-confirmed byte-identical to DESIGN.md@deeffb1:2062-2065, a
faithfully-migrated PRE-EXISTING anchor (regexes verbatim, only path
retargeted), NOT split-introduced — RATIFY-or-tidy at audit; (b) a
now stale-direction intra-prose 'see Str ABI below' cross-ref in
float-semantics.md — audit-adjudication candidate. Plan defect noted:
Task 9 Step 4's verbatim acceptance grep used a ^./ anchor not
matching the system's grep -rIn output; substance re-verified CLEAN.

Spec grounding-check PASS x2. Journals INDEX + decision-records
pointer appended (Boss-only).

crates/ail/tests/eq_ord_e2e.rs

@@ -86,8 +86,10 @@ fn eq_ord_user_adt_eq_intbox_hash_stable() {
     let mono = monomorphise_workspace(&ws).expect("mono");
 
     // The mono symbol for `eq` at a user-defined ADT uses the
-    // `<method>__<8-hex-prefix>` mangling per DESIGN.md
-    // §"Mangling scheme" (primitives use the bare type name; compound
+    // `<method>__<8-hex-prefix>` mangling (mangling is code-SoT —
+    // see the `mangling` row in design/INDEX.md / the
+    // crates/ailang-codegen/src/lib.rs //! header) (primitives use
+    // the bare type name; compound
     // / user-defined types use the 8-hex BLAKE3 prefix of the
     // canonical type bytes). We look up the single `eq__` symbol
     // synthesised at `IntBox` — there is only one user instance,
@@ -107,8 +109,9 @@ fn eq_ord_user_adt_eq_intbox_hash_stable() {
         .expect("eq__<IntBox-hash> not synthesised");
 
     // The 8-hex-prefix in the mono-symbol name is the BLAKE3 prefix
-    // of the canonical IntBox type bytes (DESIGN.md §"Mangling
-    // scheme"). Drift here means either the canonical-form encoding
+    // of the canonical IntBox type bytes (mangling is code-SoT — see
+    // the `mangling` row in design/INDEX.md). Drift here means either
+    // the canonical-form encoding
     // changed or the type's canonical bytes changed — both warrant
     // investigation before re-pinning.
     assert_eq!(