Register the inference requirements, and format the fill test

Two CI gates have failed on every push since 0.13.4 and both are
fixed here.

The traceability gate rejected `FR-INF-1` as an orphan: settings.slint
and dr-ui tag it, but the four register entries inference.md §12 wrote
were never carried into requirements.md, which is the only file the
extractor reads. §3.12 and §4.10 now hold FR-INF-1..3 and NFR-INF-1
verbatim, with the acceptance milestones pointed back at inference.md.
The matrix is regenerated (188 defined, 155 covered) and the README's
"where it stands" line, which the 0.13.6 release commit skipped, says
0.13.6 and the new figures.

`cargo fmt --check` failed on the `fill_border` call in dr-pano's
padding test, which is the first thing the Desktop job runs after
installing the toolchain and why it failed within a minute.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

README.md

@@ -76,8 +76,8 @@ controls, its place in the chain and its tests.
 
 ## Where it stands
 
-**0.13.5**, nineteen tagged releases in. 184 numbered requirements in
-scope, 84% of them claimed by code and [traced to it](docs/traceability.md);
+**0.13.6**, twenty tagged releases in. 188 numbered requirements in
+scope, 82% of them claimed by code and [traced to it](docs/traceability.md);
 the rest are written down rather than merely absent.
 
 **Not built:** plugins (post-v1, [D12](docs/requirements.md)), compare and