feat(test): add skill for picking Makefile test targets

Discovers test* targets from the Makefile instead of guessing a runner,
so the project's env vars and build prerequisites are not bypassed, and
offers them as a selection list.

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

skills/test/SKILL.md

@@ -0,0 +1,77 @@
+---
+name: test
+description: >
+  Discover the test targets of the project's Makefile, let the operator pick
+  which ones to run, then run them and report. Trigger on /test or when the
+  operator asks to run the tests, the test suite, or a specific test target
+  without naming the exact command. Portable across projects.
+---
+
+The Makefile is the source of truth for how this project runs tests. Never
+invent a command (`pytest`, `npm test`, `go test`) while a Makefile target
+exists - the target carries the project's env vars, build dependencies and
+container setup.
+
+## Step 1: find the targets
+
+From the repository root:
+
+```bash
+grep -nE '^test[A-Za-z0-9_.-]*:' Makefile
+```
+
+Read the matched rules plus their prerequisites, so the selection list can say
+what each one actually does (delegated script, container build, sub-targets).
+
+Edge cases, handled explicitly rather than guessed around:
+
+- **No Makefile**: say so in one line, name the test runner the project does
+  use (from `pyproject.toml`, `package.json`, `tox.ini`, CI workflow), and ask
+  before running anything.
+- **No `test*` target**: report the targets that do exist and stop.
+- **Included makefiles** (`include foo.mk`): grep those too.
+- **Aggregate targets**: a target whose recipe is only other test targets (e.g.
+  `test: test-unit test-integration`) is the "run everything" entry - mark it as
+  such in the list, do not expand it into its parts silently.
+
+## Step 2: offer the selection
+
+Ask with `AskUserQuestion`, `multiSelect: true`, one question. Options are the
+discovered targets, each with a one-line description of what it runs. Order the
+aggregate/full target first and label it as the complete suite.
+
+The tool takes at most 4 options. With more targets than that:
+
+- print the **complete** discovered list as text first, one line per target, so
+  nothing is hidden, then
+- offer the 4 most useful entries (aggregate first, then the ones matching the
+  operator's stated intent or the files currently uncommitted), and note that
+  "Other" accepts any target name from the printed list.
+
+Never silently truncate. If the operator already named a target in their
+request, skip the question and run it.
+
+## Step 3: run
+
+Run the selected targets in the order the operator listed them, one `make`
+invocation per target, each as its own command so a failure is attributable:
+
+```bash
+make <target>
+```
+
+Do not add `-k`, do not reorder, do not substitute a faster equivalent. If a
+target needs a long timeout (container builds, e2e), set it on the Bash call
+rather than backgrounding blindly.
+
+Stop after the first failing target unless the operator asked for all of them -
+a later suite running against a broken build produces noise, not information.
+
+## Step 4: report
+
+Per target: pass/fail plus the failing test names and the exact error output,
+quoted verbatim. Never paraphrase a failure. Then one line with the exact
+command to reproduce the failure alone.
+
+Do not fix what failed unless the operator asks - report first. If the operator
+does ask for a fix, apply the `triage` skill to it.