test: reorganize suite into unit/integration/canaries directories

Replace the hand-maintained INTEGRATION_NAMES classifier (and the
bespoke run_tests.py around it) with a directory-driven split:

  tests/unit/         unit tests, always run
  tests/integration/  Docker-dependent, skip cleanly without Docker
  tests/canaries/     upstream-regression checks, opt-in via
                      CLAUDE_BOTTLE_RUN_CANARIES=1

The pinned-pipelock-image check moves to the canary suite — it tests
upstream packaging, not our code, so it shouldn't gate every dev push.
A scheduled canaries.yml workflow runs it weekly.

The manifest-runtime tests collapse the four assertRaises cases for
distinct 'runtime' values into one subTest loop and drop the
error-message-wording assertions; the contract is "any value is
rejected", not "the error literally contains 'auto-detect'".

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/test.yml

@@ -1,10 +1,14 @@
-# Run the project's full test suite on every PR push and on push to main.
+# Run the project's test suite on every PR push and on push to main.
 #
-# The suite uses stdlib `unittest` (see tests/run_tests.py) — no external
-# Python dependencies are required to execute it. Integration tests need a
-# reachable Docker daemon; if Docker is unavailable on the runner those
-# tests skip cleanly via tests/_docker.py:skip_unless_docker, so the job
-# still passes (with skips visible in the run output).
+# The suite uses stdlib `unittest` discovery — no external Python
+# dependencies are required to execute it. Tests are split by directory:
+#
+#   tests/unit/         — pure unit tests; always run
+#   tests/integration/  — need a reachable Docker daemon; skip cleanly
+#                         (via tests/_docker.py:skip_unless_docker) when
+#                         Docker isn't available on the runner
+#   tests/canaries/     — upstream regression canaries; run on a separate
+#                         schedule (see canaries.yml), not here
 #
 # This workflow assumes the Gitea Actions runner exposes the host Docker
 # socket to the job container so `docker` commands inside the job can
@@ -20,8 +24,21 @@ on:
   pull_request:
 
 jobs:
-  test:
-    name: run tests/run_tests.py
+  unit:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Run unit tests
+        run: python3 -m unittest discover -t . -s tests/unit -v
+
+  integration:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -41,5 +58,5 @@ jobs:
             echo "docker not on PATH — integration tests will skip"
           fi
 
-      - name: Run full test suite
-        run: python3 tests/run_tests.py
+      - name: Run integration tests
+        run: python3 -m unittest discover -t . -s tests/integration -v