feat(helper): add interactive Q&A helper command

Add `markitect helper <QUESTION>` CLI command that answers questions
about markitect using its own documentation as LLM context. Uses
OpenRouter with openrouter/aurora-alpha by default; model is
configurable via --model flag or MARKITECT_HELPER_MODEL env var.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

markitect/helper/cli.py

@@ -0,0 +1,101 @@
+"""
+CLI command for the markitect helper.
+"""
+
+import os
+import sys
+
+import click
+
+from markitect.helper.knowledge import collect_knowledge
+
+DEFAULT_PROVIDER = "openrouter"
+DEFAULT_MODEL = "openrouter/aurora-alpha"
+MODEL_ENV_VAR = "MARKITECT_HELPER_MODEL"
+
+SYSTEM_PROMPT_TEMPLATE = (
+    "You are a MarkiTect expert assistant. Answer the user's question "
+    "based on the following MarkiTect documentation. Be concise and "
+    "accurate. If the documentation does not cover the question, say so.\n\n"
+    "{knowledge}"
+)
+
+
+@click.command("helper")
+@click.argument("question", nargs=-1, required=True)
+@click.option(
+    "--provider", "-p",
+    default=DEFAULT_PROVIDER,
+    type=click.Choice(["openrouter", "claude-code", "gemini", "openai"]),
+    show_default=True,
+    help="LLM provider to use.",
+)
+@click.option(
+    "--model", "-m",
+    default=None,
+    help=(
+        f"Model name. Overrides {MODEL_ENV_VAR} env var and the default "
+        f"({DEFAULT_MODEL})."
+    ),
+)
+def helper_command(question, provider, model):
+    """Ask a question about MarkiTect and get an answer from the docs.
+
+    \b
+    Examples:
+        markitect helper "What is markitect?"
+        markitect helper How do schemas work
+        markitect helper -m anthropic/claude-sonnet-4 "Explain templates"
+    """
+    from markitect.llm import create_adapter
+    from markitect.llm.exceptions import LLMConfigurationError, LLMError
+    from markitect.prompts.execution.models import RunConfig
+
+    # Join multi-word question into a single string.
+    question_text = " ".join(question)
+    if not question_text.strip():
+        click.echo("Error: empty question.", err=True)
+        sys.exit(1)
+
+    # Resolve model: --model flag > env var > default.
+    resolved_model = model or os.environ.get(MODEL_ENV_VAR) or DEFAULT_MODEL
+
+    # Build knowledge context.
+    click.echo("Loading markitect knowledge base...", err=True)
+    knowledge = collect_knowledge()
+    if not knowledge:
+        click.echo("Warning: no documentation files found.", err=True)
+
+    system_prompt = SYSTEM_PROMPT_TEMPLATE.format(knowledge=knowledge)
+
+    # Create adapter.
+    try:
+        adapter = create_adapter(
+            provider=provider,
+            model=resolved_model,
+            system_prompt=system_prompt,
+        )
+    except LLMConfigurationError as exc:
+        click.echo(f"Configuration error: {exc}", err=True)
+        if "api" in str(exc).lower() or "key" in str(exc).lower():
+            click.echo(
+                "Hint: set OPENROUTER_API_KEY (or the relevant provider key) "
+                "in your environment.",
+                err=True,
+            )
+        sys.exit(1)
+
+    # Execute the question.
+    click.echo(f"Asking {provider} ({resolved_model})...", err=True)
+    try:
+        config = RunConfig(
+            model_name=resolved_model,
+            max_tokens=4000,
+            temperature=0.3,
+        )
+        response = adapter.execute_prompt(question_text, config)
+    except LLMError as exc:
+        click.echo(f"LLM error: {exc}", err=True)
+        sys.exit(1)
+
+    click.echo(response.content)