feat(product-management): add brainstorming skill and /brainstorm command

[narenkatakam]

Summary

• Adds a product-brainstorming skill and /brainstorm command to the product-management plugin
• Fills a gap in the PM workflow: the plugin covers structured outputs (specs, roadmaps, stakeholder updates) but has no support for the divergent thinking that precedes them
• Designed as a conversational sparring partner, not a template filler — brainstorming is a dialogue, not a deliverable

What's new

1 new command

Command	What It Does
/brainstorm	Brainstorm a product idea, problem space, or strategic question with a sharp thinking partner

1 new skill

Skill	What It Covers
product-brainstorming	Brainstorming modes (problem exploration, solution ideation, assumption testing, strategy), PM frameworks (HMW, JTBD, First Principles, SCAMPER, Opportunity Solution Trees, Reverse Brainstorming), session structure, thinking partner behaviors, anti-patterns

README updated

• Added brainstorming to "What It Does" section
• Added /brainstorm to Commands table
• Added product-brainstorming to Skills table
• Added "Brainstorming a Product Idea" example workflow

Why this matters

Every PM brainstorms before they spec. The current plugin workflow jumps from "I have a vague problem" straight to /write-spec or /roadmap-update. In practice, there's a critical thinking phase in between — exploring the problem space, generating multiple approaches, challenging assumptions, and stress-testing ideas. That's what /brainstorm provides.

The skill covers:

• 4 brainstorming modes: problem exploration, solution ideation, assumption testing, strategy exploration — each with specific behaviors and useful questions
• 6 PM frameworks: How Might We, Jobs-to-be-Done, Opportunity Solution Trees, First Principles, SCAMPER, Reverse Brainstorming — used as thinking tools, not templates
• Session structure: Frame → Diverge → Provoke → Converge → Capture
• Thinking partner behaviors: when to push back, when to match energy, when to name traps
• Anti-patterns: solutioning before framing, feature parity trap, anchoring on constraints, analysis paralysis

Relationship to PR #55

PR #55 adds /feature-ideation which structures raw ideas into validated feature concepts. /brainstorm is complementary — it sits upstream in the workflow:

Problem space → /brainstorm (diverge, explore) → Ideas → /feature-ideation (converge, structure) → /write-spec (document)

No overlap — brainstorming generates the raw thinking; feature ideation structures it.

What's NOT changed

• .claude-plugin/plugin.json — no manifest changes
• CONNECTORS.md — existing connector categories already cover brainstorming needs (knowledge base, analytics, project tracker, chat)
• .mcp.json — no new MCP connections
• LICENSE — unchanged
• All existing commands and skills — untouched

Design decisions

• Conversational, not generative. Unlike /write-spec which produces a document, /brainstorm runs an interactive session. The command workflow reflects this — it closes with a summary only when the conversation reaches a natural stopping point.
• Consistent style. Follows existing patterns: YAML frontmatter, connectors banner, numbered workflow steps, ~~category tool references with graceful fallback, skill cross-references, Tips section.
• Skill depth. ~11K characters with frameworks, practical guidance, anti-patterns, and session structure — matching the depth of competitive-analysis and user-research-synthesis.
• Cross-references other commands. The Follow Up section connects to /write-spec, /synthesize-research, /competitive-brief, and /one-pager — positioning brainstorming as the upstream thinking that feeds into structured PM outputs.

Files changed

New files (2):

• product-management/commands/brainstorm.md
• product-management/skills/product-brainstorming/SKILL.md

Modified files (1):

• product-management/README.md — added brainstorming to tables, descriptions, and examples

Test plan

• Command has valid YAML frontmatter with description and argument-hint
• Skill has valid YAML frontmatter with name and description
• All ~~category references in the command match categories in CONNECTORS.md
• Skill cross-references point to existing skills (product-brainstorming)
• Command follows existing style (connectors banner, numbered steps, tips)
• Skill has sufficient depth (~11K characters)
• README tables updated consistently (What It Does, Commands, Skills, Example Workflows)
• No existing content modified or removed (only additive)