fix(check): tolerate an unverifiable check instead of dying on it

bin/check-mcp-env exits 2 for "could not run" -- no jq, or no env-file --
and the gate was written to report that as a NOTE rather than fail:

    "$DIR/check-mcp-env" "$DIR/.mcp.json" "$HOME/.op-env"
    case $? in 0) ;; 2) echo "NOTE: ..." ;; *) fail=1 ;; esac

That tolerance never executed. Task runs each cmds block under `sh -e`, so
a bare command exiting non-zero aborts the shell before `case $?` is
reached. main went red on the very commit that added the check (run #57),
with `task: Failed to run task "check": exit status 2`.

It passed locally because this host has both jq and ~/.op-env, so the
check exited 0 and the untested branch never ran. CI has neither. A
tolerated exit code that is only tolerated where it never fires is not
tolerated at all.

`|| rc=$?` puts the invocation in a compound command, which `set -e`
exempts, so `case` is reached. Both exit-2 paths verified: no env-file
(the new test's precondition) and no jq (PATH sandbox, same SKIP message
CI printed).

The test pins the tolerance itself rather than the checker: it points HOME
at an empty directory, which is exactly CI's condition, and asserts `task
check` exits 0 AND still says it could not verify -- silence would mean
skipped rather than tolerated.

Bump-Type: patch

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "skills",
   "description": "Mathias's engineering skills library, plus the hooks and MCP servers that make it enforceable: TDD, clean code, debugging, specs, discovery, CI, and secret hygiene.",
-  "version": "0.19.0",
+  "version": "0.19.1",
   "author": {
     "name": "Mathias",
     "url": "https://git.d-ma.be/mathias"