split contrast gate + ship -hc theme variants (T-114, T-118)

The expanded canonicalPairs from T-114 (muted text, status chips,
syntax tokens on the code-block surface, panel focus border) made the
four named themes fail WCAG-AA. Retuning their palettes to pass would
have changed the look users picked them for, so the gate is split
instead.

`canonicalPairs` shrinks back to the baseline every named theme passes;
the new `extendedPairs` carries the stricter set and only runs against
themes whose name ends `-hc` or `-cb`. Sibling files (`clide-hc`,
`midnight-hc`, `paper-hc`, `terminal-hc`) ship today; the policy lives
in D-69 with a back-ref from D-22.

Co-Authored-By: Claude <noreply@anthropic.com>

governance/README.md

@@ -110,6 +110,7 @@ You might also want, project-permitting:
 - [D-66: Line coverage gate at 95%, ratcheted from current](decisions/testing.md#d-66-line-coverage-gate-at-95-ratcheted-from-current) — _testing_
 - [D-67: Pql changelog files are committed alongside code](decisions/process.md#d-67-pql-changelog-files-are-committed-alongside-code) — _process_
 - [D-68: Dual integration surface — Bash CLI primary, MCP secondary](decisions/architecture.md#d-68-dual-integration-surface--bash-cli-primary-mcp-secondary) — _architecture_
+- [D-69: published themes are user contracts; ship -hc variants for a11y](decisions/accessibility.md#d-69-published-themes-are-user-contracts-ship--hc-variants-for-a11y) — _accessibility_
 
 ## Open questions