design/ + source rustdoc: replace opaque shorthand with content phrases + links

Reader-facing prose and rustdoc carried opaque shorthand like
"Decision 10", "clause-5", "mq.1", "ct.1", "eob.1", "rpe.1",
"post-mq.3", and "Iter 22b.1:" with no in-repo definition the reader
could follow. This commit replaces every such occurrence in the
durable tier the reader is most likely to land on (design/ ledger +
source //! module headers + the central /// public-item rustdoc) with
an inline content phrase plus, where applicable, a Markdown link to
the file that defines the referenced concept.

design/ ledger — 16 files:
  Definition-site headings demoted from "Decision N: <title>" to
  "<title>": authoring-surface, tail-calls, memory-model section in
  rc-uniqueness.md, dual-allocator section, typeclass design,
  effects "pure core + algebraic effects".
  Cross-reference sites: "Decision 1" -> canonical-schema principle
  (data-model); "Decision 3/4" -> effects + scope-boundaries; "Decision
  6" -> authoring-surface; "Decision 8" -> tail-calls; "Decision 9" ->
  rc-uniqueness (dual-allocator); "Decision 10" -> memory-model;
  "Decision 11" -> typeclasses (model). "clause-5" -> body-link
  durability gate. "clause-3" (in language-constraints) ->
  bug-class-reintroduction discriminator. "mq.1/2/3", "ct.1/4",
  "eob.1", "rpe.1" -> the canonical-form rule / the type-driven
  dispatch / the Str carve-out / etc. "post-mq.3" -> "type-driven".

design/contracts/feature-acceptance.md: file-local "clauses 1/2/3"
-> "criteria 1/2/3" (sprachliche Kohärenz mit der File-Überschrift
"Feature-acceptance criterion"); "the clause-3 mechanism" -> "the
bug-class-reintroduction discriminator".

Source //! module headers — 24 files:
  Stripped "Iter X.Y:" prefixes and "(Decision N)" / "(mq.X)" tags
  from spec_drift, uniqueness, reuse_shape, migrate_canonical_types,
  typeclass_22b{2,3,c}, suppress_filter, lift, mono, linearity,
  diagnostic, method_dispatch_pin, method_collision_pin,
  no_per_type_print_ops, mq3_multi_class_e2e, print_mono_body_shape,
  print_no_leak_pin, cli_diag_human_workspace_load_error,
  ct1_check_cli, prose snapshot, unbound_in_instance_method_pin,
  mono_xmod_ctor_pattern, desugar.

Central /// public-item rustdoc:
  ast.rs (full sweep — every "Iter X" + "Decision N" prefix
  reformulated; mode/Type::Fn rustdoc now points at memory-model.md;
  Constraint / SuperclassRef / InstanceDef / ClassDef rustdoc points
  at typeclasses contract).
  diagnostic.rs (all "(Iter X)" / "(mq.X)" tags on diagnostic codes
  removed).
  lib.rs (FORM_A_SPEC rustdoc points at authoring-surface.md
  instead of "Decision 6").
  canonical.rs (type_hash + Float-literal rustdoc).

Still outstanding (for a follow-up commit): ~500 inline `//`
code-body comments with `Iter X.Y` markers across the workspace, and
a handful of `///` rustdoc items in hash_pin / workspace_pin / lift /
mono / suppress_filter test-pin and internal-function bodies. Code
identifiers (test filenames like `mq3_multi_class_e2e.rs`, function
names like `iter18e_drop_iterative_default_preserves_hashes`) stay
verbatim per the user's "code identifiers stay verbatim" rule.

Tests: design_index_pin 5/5 + docs_honesty_pin 5/5; workspace builds
clean; full `cargo test --workspace` previously green (every
`test result: ok` line, no FAILED line).

design/contracts/method-dispatch.md

@@ -6,14 +6,16 @@ The class-method resolution rule that pairs with the
 [typeclasses](typeclasses.md) contract; the `Show`/`Eq`/`Ord` instances
 the rule dispatches against live in [prelude classes](prelude-classes.md).
 
-Post-mq.3, dispatch is two-mode:
+Dispatch is two-mode:
 
 **Polymorphic call sites** (inside a fn body with `forall` +
 constraint set): the constraint names the class via the qualified
-`Constraint.class` field (canonical-form per mq.1). Synth's
-residual carries the class name directly; constraint-discharge at
-fn-body-end matches against the workspace registry by
-`(class, type_hash)` key.
+`Constraint.class` field (canonical form: bare for same-module,
+`<module>.<Class>` for cross-module; see
+[memory model](memory-model.md) for the canonical-form rule).
+Synth's residual carries the class name directly;
+constraint-discharge at fn-body-end matches against the workspace
+registry by `(class, type_hash)` key.
 
 **Monomorphic call sites**: synth consults the workspace-flat
 `Env.method_to_candidate_classes: BTreeMap<MethodName,
@@ -42,7 +44,7 @@ dispatch rule:
 The `method_to_candidate_classes` index is the load-bearing data
 structure for this routing — its construction in `build_check_env`
 inverts the per-module `class_methods` maps (themselves tuple-keyed
-by `(qualified-class, method)` post-mq.3) to a workspace-flat
+by `(qualified-class, method)`) to a workspace-flat
 method-name-to-class-set map.
 
 Class-fn collisions resolve at the call site, not at workspace load