docs: add concept notes and rename execution plan

[PacemakerG]

What changed

• Add a Go fundamentals note comparing Go with C++ and Python.
• Add writing guidance for concept documents.
• Rename the AgentDock execution plan file without changing its contents.

Why

Publish the current local docs updates to the AgentDocks repository.

Impact

Documentation only; no runtime or dependency changes.

Checks

• git diff --cached --check
• Verified the execution-plan rename is 100% content-preserving.
• Checked the public documentation tree for common credential patterns; no matches found.
• Excluded the unrelated reference/agent-sandbox working-tree change.