fix(infra): run orchestrator containers as host uid 1000:1000 (not root)

Both compose services (orchestrator, orchestrator-staging) now declare
user: "1000:1000" so pipeline artifacts (git worktree, docs/work-items
commits) are created as slin:slin on the host — git pull/reset under slin
no longer fail with permission errors. docker.sock access preserved via
group_add: ["999"]. SSH mount target aligned with the launcher-forced
HOME=/home/slin (/root/.ssh -> /home/slin/.ssh). launcher.py and Dockerfile
unchanged. INFRA.md and CHANGELOG.md updated; host-prerequisites (P-1..P-4)
documented.

Refs: ORCH-040

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

docker-compose.yml

@@ -3,6 +3,11 @@ services:
     build: .
     container_name: orchestrator
     restart: unless-stopped
+    # ORCH-040: бежим под uid:gid хоста (slin=1000:1000), а не root, чтобы
+    # артефакты конвейера (worktree + docs) создавались как slin:slin и git на
+    # хосте работал без ручного chown. Доступ к docker.sock сохранён через
+    # group_add: ["999"] (МИНА 1 — НЕ удалять). См. ADR-001 ORCH-040.
+    user: "1000:1000"
     # init: true injects docker-init (tini) as PID 1 so reparented grandchild
     # processes from the claude/node subprocess tree are reaped (no zombies, B-2).
     init: true
@@ -15,7 +20,8 @@ services:
       - /usr/bin/node:/usr/bin/node:ro
       - /home/slin/.claude:/home/slin/.claude
       - /home/slin/.claude.json:/home/slin/.claude.json:ro
-      - /home/slin/.orchestrator-ssh:/root/.ssh:ro
+      # ORCH-040: target согласован с HOME=/home/slin (launcher), не /root/.ssh.
+      - /home/slin/.orchestrator-ssh:/home/slin/.ssh:ro
     env_file: .env
     environment:
       - ORCH_REPOS_DIR=/repos
@@ -35,6 +41,8 @@ services:
     build: .
     container_name: orchestrator-staging
     restart: unless-stopped
+    # ORCH-040: тот же uid хоста, что и у prod (см. комментарий выше / ADR-001).
+    user: "1000:1000"
     init: true
     network_mode: host
     command: ["uvicorn", "src.main:app", "--host", "0.0.0.0", "--port", "8501"]
@@ -46,7 +54,8 @@ services:
       - /usr/bin/node:/usr/bin/node:ro
       - /home/slin/.claude:/home/slin/.claude
       - /home/slin/.claude.json:/home/slin/.claude.json:ro
-      - /home/slin/.orchestrator-ssh:/root/.ssh:ro
+      # ORCH-040: target согласован с HOME=/home/slin (launcher), не /root/.ssh.
+      - /home/slin/.orchestrator-ssh:/home/slin/.ssh:ro
     env_file: .env.staging
     environment:
       - ORCH_REPOS_DIR=/repos