feat: add /mgw:ask contextual question routing command

[snipcodeit]

Summary

• Add /mgw:ask <question> slash command that classifies questions/observations during milestone execution into five categories: in-scope, adjacent, separate, duplicate, or out-of-scope
• Spawns a general-purpose classification agent with full project context (milestone, all issues, active state, recent git diff) that reads code/state and returns a structured classification report
• Offers category-specific follow-up actions: file new issue (separate), post comment on related issue (adjacent), note for backlog (out-of-scope)
• Updates help.md with new Query command section and all four workflow consumer tables

Closes #38

Milestone Context

• Milestone: v1 — Pipeline Intelligence
• Phase: 8 — Query Layer
• Issue: 4 of 4 in milestone

Changes

• commands/ask.md — New slash command definition (question classification agent, 5 classification categories, follow-up actions)
• .claude/commands/mgw/ask.md — Mirror of commands/ask.md
• commands/help.md — Add Query section with /mgw:ask entry
• .claude/commands/mgw/help.md — Mirror of commands/help.md
• .claude/commands/mgw/workflows/gsd.md — Add question classification agent pattern, update consumers table
• .claude/commands/mgw/workflows/validation.md — Add ask.md to delegation boundary consumers table
• .claude/commands/mgw/workflows/state.md — Add ask.md to validate_and_load and project state consumers
• .claude/commands/mgw/workflows/github.md — Add ask.md to issue operations and mutations consumers

Test Plan

• Run /mgw:ask "test question" and verify classification agent spawns with full context
• Verify project.json is loaded and milestone/issue context is passed to agent
• Verify .mgw/active/ state files are loaded for active work context
• Verify git diff output is included in agent context
• Verify classification output matches one of: in-scope, adjacent, separate, duplicate, out-of-scope
• Verify "separate" classification offers to file a new issue via gh issue create
• Verify "adjacent" classification offers to post a comment on the related issue
• Verify help.md shows /mgw:ask under new Query section
• Verify commands/ask.md and .claude/commands/mgw/ask.md are identical mirrors
• Verify delegation boundary: orchestrator reads state only, agent reads code/state