refactor(template): match single-harness (hyperguild) architecture (infra#178)

The template carried the old multi-tool/agentsquad-era CAD-executor scaffold.
Refresh it to the consolidated single-harness reality (hyperguild#75/#76):
Claude Code + hyperguild, session-based, brain + gitea MCP. No dispatch
automation added (out of scope — dispatch stays manual until real friction
warrants it).

Removed (multi-tool + dead generator + deployed-agent-era):
- .aider.conf.yml, .aider.conventions.md, .cursorrules
- .context/ (mcp.json, PROJECT.md, system-prompt.txt)
- agent-policy.yaml (k8s NetworkPolicy scaffold)
- scripts/context-sync.sh (generated the above from .context/PROJECT.md — now
  input-less) + its context:sync* Taskfile tasks

Added / updated:
- .mcp.json (root, hyperguild-shaped: brain + gitea, Bearer env tokens)
- CLAUDE.md / AGENTS.md / README.md → single-harness workflow (issue →
  hyperguild session → PR → report-back comment → brain capture)
- AGENT_BOUNDARIES.md kept (harness-agnostic egress/scope guidance); repointed
  its two references to the removed agent-policy.yaml

Left alone: cd.yml, Dockerfile, Taskfile (build/test), go.mod, cmd/, internal/,
pkg/, .claude/. No dangling refs to removed files (verified). Refs infra#178.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Taskfile.yml

@@ -23,14 +23,3 @@ tasks:
       - golangci-lint run ./...
       - go vet ./...
       - go test ./... -race -count=1
-
-  context:sync:
-    desc: Regenerate all harness-specific context files
-    cmds:
-      - bash scripts/context-sync.sh
-  context:sync:claude:
-    cmds: [bash scripts/context-sync.sh claude]
-  context:sync:agents:
-    cmds: [bash scripts/context-sync.sh agents]
-  context:sync:cursor:
-    cmds: [bash scripts/context-sync.sh cursor]