Add ReinOpenWeights adapter, closing GLAS-WP-0001-T05

glas_harness/reins/rein_openweights.py implements the Rein ABC by
shelling out to `rein-openweights run --task-file ... --no-hub
[--model ...]`, mirroring reins/rein_aharness.py exactly. Factored the
duplicated git_head/write_task_file logic into reins/_shared.py, used
by both adapters now. registry/reins/rein-openweights.yaml flipped to
status: implemented. 8 new tests (mocked subprocess), 18/18 passing.

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

workplans/GLAS-WP-0001-harness-router-foundation.md

@@ -103,16 +103,19 @@ is pushed — coordinate repo creation with the operator.
 `rein-openweights/REIN-OW-WP-0001` (T01-T04) is done: standalone agentic
 loop, own OpenRouter client (not llm-connect — see that workplan's T01
 for why), tool surface, credential acquisition, commit-verified success
-+ hub reporting, 26 tests. **Not yet done here:** a
-`glas_harness/reins/rein_openweights.py` adapter implementing the `Rein`
-ABC and shelling out to `rein-openweights run`, mirroring
-`reins/rein_aharness.py` — that's the piece that actually plugs this
-rein into glas-harness's gateway. registry/reins/rein-openweights.yaml's
-`status: planned` should flip to `implemented` once that adapter lands.
++ hub reporting, 26 tests.
+
+`glas_harness/reins/rein_openweights.py` now implements the `Rein` ABC
+by shelling out to `rein-openweights run --task-file ... --no-hub
+[--model ...]`, mirroring `reins/rein_aharness.py` exactly (both now
+share `reins/_shared.py` for `git_head`/`write_task_file` — the
+duplication was real, so it got factored out). `registry/reins/
+rein-openweights.yaml` flipped to `status: implemented`. 8 new tests,
+all mocked.
 
 ```task
 id: GLAS-WP-0001-T05
-status: progress
+status: done
 priority: high
 state_hub_task_id: "84fa62ae-3b34-42fd-a263-f65c35e87586"
 ```