feat(register): register llm-security-commons as shared-asset

The org's 21st repo (register: 20 → 21, forge: 21 — confirmed by --refresh
last session). Class verified structurally, mirroring c5c11f4: absent from
the catalog's marketplace.json, no .claude-plugin/, README.md + LICENSE
present, `## Non-goals` heading present, consumed by `llm-security` (which
already carries the `security` trait) as a git subtree per its own README
Install section. So `vendor` is the right install form.

Trait left unset: llm-security-commons' own STATE.md names this as an open
operator decision, and the register's trait definition keys traits to what
code DOES — this repo states "no runnable code, data/specifications/
fixtures only."

Measured, not assumed:
- llm-security-commons now gates ERROR (10x LINK-INTERNAL-MISSING) — its
  README documents the target directory layout (lexicon/, codepoints/,
  signatures/, calibration/, mapping/, schema/, spec/, conformance/) but
  `git ls-files` shows only signatures/active-content.json and
  docs/extraction-plan.md exist; neither was flagged, so the check found
  real gaps, not noise. Findings recorded, not fixed here — that repo's
  own session owns them.
- llm-security (the plugin that vendors this) still reports zero ERROR:
  no `open/llm-security-commons` reference exists anywhere in the org
  outside the commons repo itself, so no dependent verdict moved. Matches
  what STATE predicted before this session started.

Not tagged as a release: catalog's ref is still on v0.3.0, two releases
(v0.4.0, v0.5.0) behind and already asked for via coord (unactioned,
latest ask reply-expected: no). Stacking a third release on top would only
widen that gap; this commit reaches installed consumers on whichever
release picks it up next, same as portfolio-optimiser-commons did in
c5c11f4 -> 43a8d28.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AjNqnudJnH4Q9ZyVWh8UDr

register/repos.json

@@ -31,6 +31,7 @@
     "ktg-plugin-marketplace": "catalog",
     "playground-design-system": "shared-asset",
     "portfolio-optimiser-commons": "shared-asset",
+    "llm-security-commons": "shared-asset",
     ".profile": "org-profile",
     "portfolio-optimiser": "standalone",
     "portfolio-optimiser-claude": "standalone",