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.env.example

@@ -0,0 +1,12 @@
+# Copy to $HOME/.codex/gitea.env and replace every example value locally.
+GITEA_URL=http://gitea.example.invalid:3000
+GITEA_TOKEN=【replace-with-minimum-scope-token】
+
+# Optional non-secret identity used to verify dispatcher-authored CLAIM comments.
+GITEA_DISPATCHER_LOGIN=【dispatcher-gitea-login】
+
+# Required only when the team explicitly accepts HTTP credential exposure risk.
+GITEA_ALLOW_INSECURE_HTTP=1
+
+# Optional: bypass local HTTP/SOCKS proxy for this Gitea instance.
+GITEA_DIRECT=1