feat(RMGR-WP-0001): complete T05 end-to-end vertical slice

Implement observe/reconcile/update-task-status CLI path: workplan parse,
JSON projection index, git-backed task status writeback with correlation
events, and E2E pytest plus evidence artifacts. Finish foundation workplan.

docs/evidence/t05-command-result.json

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+{
+  "command": "repo.work.update_task_status",
+  "status": "applied",
+  "correlation_id": "3a152f55-acca-41de-a310-d388ddf5a1d1",
+  "evidence": {
+    "status": "applied",
+    "git_sha": "0b71f90b7782255e1e15b0def16d15299ca09e15",
+    "files_touched": [
+      "workplans/DEMO-WP-0001.md"
+    ],
+    "observed_at": "2026-08-09T20:49:14.382153+00:00",
+    "index_path": "/tmp/rmgr-e2e-1946474/.repo-manager/index.json"
+  }
+}

docs/evidence/t05-e2e-proof.json

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+{
+  "task": "RMGR-WP-0001-T05",
+  "fixture": "live-proof temp repo",
+  "before_sha": "1e8623d758b7c4599bb0c48bb9450990a1a948a1",
+  "after_sha": "0b71f90b7782255e1e15b0def16d15299ca09e15",
+  "command_result": {
+    "command": "repo.work.update_task_status",
+    "status": "applied",
+    "correlation_id": "3a152f55-acca-41de-a310-d388ddf5a1d1",
+    "evidence": {
+      "status": "applied",
+      "git_sha": "0b71f90b7782255e1e15b0def16d15299ca09e15",
+      "files_touched": [
+        "workplans/DEMO-WP-0001.md"
+      ],
+      "observed_at": "2026-08-09T20:49:14.382153+00:00",
+      "index_path": "/tmp/rmgr-e2e-1946474/.repo-manager/index.json"
+    }
+  },
+  "git_log": "0b71f90b7782255e1e15b0def16d15299ca09e15 repo.work.update_task_status DEMO-WP-0001-T01 -> done"
+}

docs/evidence/t05-vertical-slice.md

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+# RMGR-WP-0001-T05 — vertical slice proof
+
+**Date:** 2026-08-09  
+**Contract:** `helixforge.repo-manager` 0.1 (subset implemented)
+
+## Slice steps
+
+| # | Requirement | Implementation | Proof |
+| --- | --- | --- | --- |
+| 1 | Represent a repository | `rmgr observe` / `observe_repository` | Snapshot JSON with slug, classification, revision |
+| 2 | Index declared work | `rmgr reconcile` → `.repo-manager/index.json` | workplan + task records from `workplans/` |
+| 3 | Emit normalized change | events on index: `repo.command.applied`, `repo.work.indexed` | event log with `correlation_id` |
+| 4 | File-backed transition | `rmgr update-task-status` | task `status:` patched in workplan file |
+| 5 | Git evidence | `gitops.commit_paths` | `evidence.git_sha` required; commit message includes correlation_id |
+| 6 | Rebuilt projection | re-observe after command | task status + head_sha match evidence |
+
+## Automated proof
+
+```bash
+cd ~/repo-manager && pytest tests/test_e2e_vertical_slice.py -q
+```
+
+## Live CLI proof
+
+Artifacts:
+
+- `docs/evidence/t05-e2e-proof.json`
+- `docs/evidence/t05-command-result.json`
+
+## Hub-core note
+
+Events are written to the local index event log in contract-shaped JSON. HTTP
+delivery to hub-core `port.events` is dual-run work (extraction P3 / hub-core
+ports), not required to prove Git authority + projection rebuild.
+
+## Limits of this slice (honest)
+
+- Projection store is **local JSON**, not Postgres yet (ADR-001 production DB still planned).
+- No FastAPI server in this slice; CLI implements the same commands.
+- Authz is not enforced (dev path); production requires policy port.
+- Single command type implemented: `repo.work.update_task_status`.