v0.75.0 — the madc::value intrinsic + value-first <ns_madc>

Release v0.75.0 — 2026-08-09

madc::value is now a first-class script intrinsic: value, var, and
qualified madc::value work with zero includes in the default dialect,
and the whole madc:: API surface is typed in it — the value-first
<ns_madc> drops its #include <string>, so madc::-only scripts
compile at the millisecond floor (the exec-channel sort script: 15ms
packed, down from ~130ms). Two long-latent compiler defects the work
uncovered ship fixed in the same release.

• value / var / madc::value — spellings of the one intrinsic
  DataDef (canonical madc::value); array unchanged (a madc::array IS
  a madc::value carrying an array). var declares the runtime-retaggable
  dynamic carrier (contrast compile-time auto). Bare spellings are
  --std=madc-only; qualified madc::value works in every mode.
• Scalar surface on the intrinsic — native operator= family
  (cstr/int/real/bool/value), c_str(), printf %s coercion, and the
  channel readline/readall/write value carriers.
• Value-first <ns_madc> — primary API in value + const char*
  (value-out eval twins with _ctx scope-capture siblings, const char*
  context keys); std::string overloads become conveniences declared
  exactly when <string> precedes <ns_madc> (auto-include orders it
  correctly for include-free scripts).
• No-viable method overloads against value parameters now diagnose
  ([over.match.viable]) instead of silently compiling the by-name arity
  pick with the wrong parameter class (a raw std::string* passed as
  madc::value*).
• Method default arguments work — [required..total] arity plus
  call-site filling from the selected overload; previously they survived
  overload selection only via the silent fallback and then failed in
  c2mir.
• Use-after-free fixed in the file-lane tokenizer — token file
  pointers are interned; libmadc's temp-source eval no longer leaves the
  lazy JIT build reading freed memory (valgrind-clean).
• Suite grows to 1017 integration tests (JIT, EXE, OBJ, release,
  packed all 0-failure) and 1013/0 on the libc++ flavor lane.

See CHANGELOG.md for full details.