Phase E: action-language tool vocabulary

Replace Claude-Code-specific tool names in skill prose, prompt
templates, and OpenCode-facing docs with action-language descriptions
that resolve to each runtime's native tool via the per-platform refs.

Changes by category:

- Prose mentions ("Use TodoWrite to track...", "Use Task tool with
  general-purpose type") → action language ("Track each item as a
  todo", "Dispatch a general-purpose subagent")

- Prompt template headers (6 files): "Task tool (general-purpose):"
  → "Subagent (general-purpose):" — preserves the type information
  without naming Claude Code's specific dispatch tool

- DOT flowchart node labels: "Invoke Skill tool" → "Invoke the
  skill"; "Create TodoWrite todo per item" → "Create a todo per
  item"

- OpenCode INSTALL.md and docs/README.opencode.md: replace the old
  "TodoWrite → todowrite, Task → @mention" mapping (which both
  taught a vocabulary skills no longer use AND was wrong about
  @mention being a real OpenCode syntax) with an action-language
  mapping verified against the installed OpenCode CLI's tool
  inventory.

The platform-tools refs landed in Phase B already document each
runtime's resolution; skills now speak in the actions those refs
map. Tool names that genuinely belong only in the per-platform
dispatch section ("In Claude Code: Use the `Skill` tool") and the
Claude-Code-specific Bash run_in_background flag note in
visual-companion remain — those are intentional carve-outs.

docs/README.opencode.md

@@ -104,12 +104,17 @@ The plugin does two things:
 
 ### Tool Mapping
 
-Skills written for Claude Code are automatically adapted for OpenCode:
+Skills speak in actions rather than naming any one runtime's tools. On OpenCode these resolve to:
 
-- `TodoWrite` → `todowrite`
-- `Task` with subagents → OpenCode's `@mention` system
-- `Skill` tool → OpenCode's native `skill` tool
-- File operations → Native OpenCode tools
+- "Create a todo" / "mark complete in todo list" → `todowrite`
+- `Subagent (general-purpose):` template → OpenCode's `task` tool with `subagent_type: "general"` (or `"explore"` for codebase exploration)
+- "Invoke a skill" → OpenCode's native `skill` tool
+- "Read a file" / "create a file" / "edit a file" → `read`, `write`, `edit`
+- "Run a shell command" → `bash`
+- "Search file contents" / "find files by name" → `grep`, `glob`
+- "Fetch a URL" / "search the web" → `webfetch`, `websearch`
+
+(Verified against the installed OpenCode CLI's tool inventory.)
 
 ## Troubleshooting