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>

.gitignore

@@ -1,7 +1,4 @@
 # ---> Go
-# If you prefer the allow list template instead of the deny list, see community template:
-# https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
-#
 # Binaries for programs and plugins
 *.exe
 *.exe~
@@ -12,16 +9,24 @@
 # Test binary, built with `go test -c`
 *.test
 
-# Output of the go coverage tool, specifically when used with LiteIDE
+# Output of the go coverage tool
 *.out
 
-# Dependency directories (remove the comment below to include it)
-# vendor/
+# Build output
+dist/
 
-# Go workspace file
-go.work
-go.work.sum
+# NOTE: go.work / go.work.sum are committed in this monorepo (core + app-modern + app-win7).
 
 # env file
 .env
 
+# Local Gitea MCP credentials and diagnostics must never enter Git.
+.codex/gitea.env
+gitea.env
+gitea.env.*
+!gitea.env.example
+*.stderr.log
+
+# Python 本地校验缓存
+__pycache__/
+*.py[cod]