Add harness coding docs for SoftBox (Go + Gio dual-build)

Initialize the full harness coding document set from the
harness_coding_docs template, customized for the SoftBox project:

- Vision, requirements, tech stack (modern Go 1.25 + Gio v0.10.1;
  Win7 legacy Go 1.20.14 + Gio v0.6.0), architecture, coding rules
- Protocol contracts (signed catalog, package protocol v1, Ed25519
  license, events, CLI) and Gio view structure
- Roadmap Phase 0-6 with 20 suggested tasks; T-001 (monorepo
  skeleton) filed and ready to claim
- Agent entry points (AGENTS.md, docs/00-ai-start-here.md),
  context manifest, governance scripts and tests
- Merge Go gitignore with harness rules; keep go.work tracked

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

.gitea/workflows/harness-governance.yml

@@ -0,0 +1,21 @@
+name: Harness governance
+
+on:
+  push:
+  pull_request:
+
+permissions: read-all
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - name: Validate templates and governance
+        run: |
+          python scripts/validate_agent_context.py
+          python -m unittest discover -s tests -p "test_*.py"
+          python scripts/validate_harness_governance.py