test(compat): extend the seam matrix to the alpha.5 and rc.1 baselines

Add the two heads of the declared 0.1.2 lines as matrix baselines: the
preview window's head (dsh-v0.1.2-alpha.5, where the DSH STORE
latest-three compatibility window currently ends) and the next-channel
release candidate (dsh-v0.1.2-rc.1). Their seam faces verified identical
to alpha.2, so the generation's client faces collapse into one shared
CLIENT_0_1_2 constant.

The new baselines surfaced a real staging drift: since 0.1.2-alpha.3 the
session-projection sources import SessionLogOffset/SessionSeq from
@deepseek-ai/dsh-session as runtime values, so the compat driver now
installs each baseline's own vendored dsh-session release next to cordis
(Baseline.session).

The release workflow fetches the two new baseline tags before testing.

docs/compatibility.md records the per-release verification evidence,
including the 2026-09-03 disposable-profile install/uninstall matrix
across 0.1.1-rc.2, 0.1.2-alpha.3/4/5 and 0.1.2-rc.1 (ref
AI-Scarlett/DSH-Store#439).

.github/workflows/release.yml

@@ -53,7 +53,9 @@ jobs:
           git remote add origin https://github.com/deepseek-ai/deepseek-harness.git
           git fetch --depth 1 -q origin \
             refs/tags/dsh-v0.1.1-rc.2:refs/tags/dsh-v0.1.1-rc.2 \
-            refs/tags/dsh-v0.1.2-alpha.2:refs/tags/dsh-v0.1.2-alpha.2
+            refs/tags/dsh-v0.1.2-alpha.2:refs/tags/dsh-v0.1.2-alpha.2 \
+            refs/tags/dsh-v0.1.2-alpha.5:refs/tags/dsh-v0.1.2-alpha.5 \
+            refs/tags/dsh-v0.1.2-rc.1:refs/tags/dsh-v0.1.2-rc.1
 
       - name: Test
         run: DSH_REPO="$PWD/.tmp/dsh-repo" pnpm test