fix(opencode): resolve MCP prompts with real arguments, not $N placeholders

[Haohao-end]

Issue for this PR

Closes #33564

Type of change

• Bug fix

What does this PR do?

MCP prompt commands sent literal $1/$2 strings as argument values to prompts/get when registering commands. Servers that validate argument types (e.g. precision: int) rejected them, logging failed to getPrompt at startup and leaving the command with an empty template.

Since listPrompts argument metadata has no type info, a type-correct placeholder can't be synthesized. Instead, resolve MCP prompt templates at invocation: store prompt metadata in Command.state and add Command.template(name, args), which calls getPrompt with the user's real positional arguments (servers coerce numeric strings). Non-MCP commands are unchanged.

How did you verify your code works?

• oxlint clean on both changed files
• types verified against the codebase (noUncheckedIndexedAccess is off, so args[i] is string)
• repro: a typed-arg MCP prompt (e.g. precision: int) no longer logs $2/$1 conversion errors at startup; invoking it with real args renders the prompt server-side

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR