fix(docs): README back-links + real LICENSE section (unblocks 2 red CI gates)

README failed two CI doc-governance gates in .github/workflows/ci.yml:

1. tools/check-soundness-ledger.sh (property 2, back-links): README pointed at
   `SOUNDNESS-LEDGER.adoc` — a filename that does not exist. The gate greps for
   `SOUNDNESS.adoc`; the old string did not match -> RED.
2. tools/check-doc-truthing.sh (DOC-04): README did not mention the authoritative
   status matrix `CAPABILITY-MATRIX.adoc` anywhere -> RED.

Fixes, all in README.adoc:
- repoint the 3 soundness-ledger references to `docs/SOUNDNESS.adoc`
- add `docs/CAPABILITY-MATRIX.adoc` (feature readiness) in Status + Documentation
- replace the stale "state the license and add a LICENSE file" TODO with a real
  License section (LICENSE + LICENSES/ already exist: MPL-2.0 code, CC-BY-SA-4.0 docs)

Supersedes #675 (which fixed only the soundness link).

Verified (dune 3.24.0, system OCaml 4.14.1 + opam switch as-verify):
  BUILD_EXIT=0
  OK: doc-truthing intact  (TRUTH_EXIT=0)
  OK: soundness ledger — all 5 properties hold  (GATE_EXIT=0)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

README.adoc

@@ -27,7 +27,8 @@ Early and experimental. This is *v0.2*: the architecture is settled, the
 implementation and the metatheory are partial and still moving. It is suitable
 for experimentation, teaching, and small sound components -- not yet for
 production. What is proven, what is implemented, and what is still prose are
-stated plainly below and tracked in `SOUNDNESS-LEDGER.adoc`.
+stated plainly below and tracked in `docs/SOUNDNESS.adoc`; per-feature
+readiness is tracked in `docs/CAPABILITY-MATRIX.adoc`.
 
 == What you get
 
@@ -142,7 +143,7 @@ risk here, and it is not yet solved.
 Soundness is *partially mechanised, and honestly tracked.* An initial,
 axiom-free, machine-checked result for code-generation preservation exists
 (Coq/Rocq). A number of residuals remain open; they are recorded -- not hidden
--- in `SOUNDNESS-LEDGER.adoc`, which states for each claim whether it is
+-- in `docs/SOUNDNESS.adoc`, which states for each claim whether it is
 mechanised or still argued in prose.
 
 The ledger is the source of truth for what currently holds. This README
@@ -192,8 +193,12 @@ totality cut, and a WebAssembly target -- rather than any one ingredient.
 == Documentation
 
 // TODO: link the design notes and the examples directory once locations are stable.
-* Soundness status: `SOUNDNESS-LEDGER.adoc`
+* Soundness status: `docs/SOUNDNESS.adoc`
+* Feature readiness: `docs/CAPABILITY-MATRIX.adoc`
 
 == License
 
-// TODO: state the license and add a LICENSE file.
+Code is licensed under the Mozilla Public License 2.0 (`MPL-2.0`); prose and
+documentation under Creative Commons Attribution-ShareAlike 4.0
+(`CC-BY-SA-4.0`). Full texts are in `LICENSE` and `LICENSES/`; per-file
+provenance is declared with SPDX headers.