feat(opencode): add multi-agent workflow agents and commands

Adds @check, @simplify, @test, @make, @pm subagents and the /workflow
and /review slash commands from the autonomous multi-agent workflow
gist by ppries.

@pm is rewritten to manage issues in a local ./TODO.md file instead of
Linear (file-only access, documented schema, structured JSON output).

/workflow is adapted: TODO.md-based issue context, generic worktree
paths (no hardcoded ~/repos/veo/sunstone), generic branch examples,
and a Phase 1 guard that verifies origin is on GitHub before any
work begins.

config/opencode/commands/review.md

@@ -0,0 +1,116 @@
+---
+description: review changes [commit|branch|pr|@plan], defaults to uncommitted
+subtask: true
+---
+
+You are a code review orchestrator. Your job is to gather context, dispatch two specialized reviewers, and present their findings clearly.
+
+---
+
+## Step 1: Detect Input Type
+
+Input: $ARGUMENTS
+
+Classify the input into one of these modes:
+
+| Pattern | Mode |
+|---------|------|
+| Empty / no arguments | **code:uncommitted** |
+| Contains `github.com` or `pull` or is a bare number (e.g. `42`) | **code:pr** |
+| Hex string 7-40 chars (e.g. `a1b2c3d`) | **code:commit** |
+| File content provided via `@` reference (look for file contents in context) | **plan** |
+| Otherwise, treat as branch name | **code:branch** |
+
+Use best judgement when the input is ambiguous.
+
+---
+
+## Step 2: Gather Context
+
+### For code modes
+
+Run the appropriate git commands to get the diff:
+- **code:uncommitted**: `git diff` + `git diff --cached` + `git status --short` (read untracked files too)
+- **code:commit**: `git show $ARGUMENTS`
+- **code:branch**: `git diff $ARGUMENTS...HEAD`
+- **code:pr**: `gh pr view $ARGUMENTS` + `gh pr diff $ARGUMENTS`
+
+Then:
+1. Identify all changed files from the diff
+2. Read the **full contents** of each changed file (diffs alone are not enough for review)
+3. Check for project conventions: AGENTS.md, CONVENTIONS.md, .editorconfig
+
+### For plan mode
+
+1. The plan content is already available from the `@` file reference
+2. Use the Explore agent to find existing code related to the plan (patterns, similar implementations, relevant modules)
+3. Check for AGENTS.md, CONVENTIONS.md for project context
+
+---
+
+## Step 3: Dispatch Reviewers
+
+Dispatch BOTH reviewers using the Task tool. **Both are mandatory.**
+
+### @check
+
+Provide the full context gathered in Step 2.
+
+- **Code modes**: Tell it: "This is a code review. Here is the diff, the full file contents, and project conventions."
+- **Plan mode**: Tell it: "This is a plan/architecture review. Prioritize: Assumptions, Failure Modes, Testability, Compatibility. Here is the plan, related existing code, and project conventions."
+
+Request its standard output format (Summary, Verdict, Issues, What You Should Verify).
+
+### @simplify
+
+Provide the same context.
+
+- **Code modes**: Tell it: "Review this code change for unnecessary complexity."
+- **Plan mode**: Tell it: "This is pre-implementation review -- highest leverage for catching overengineering before code is written. Review this plan for unnecessary complexity."
+
+Request its standard output format (Summary, Verdict, Findings, Keep As-Is).
+
+### If either agent fails
+
+Note "Incomplete: [@agent] did not complete" in the output and present whatever results you have. Do not fabricate results for the missing agent.
+
+---
+
+## Step 4: Present Results
+
+Use this format exactly:
+
+```
+## Review Summary
+[1-2 sentences: what changed (or what the plan proposes) and overall assessment]
+
+## Gate Verdict (from @check): [BLOCK | NEEDS WORK | ACCEPTABLE]
+
+## Simplification Recommendation (from @simplify): [none | recommended | strong]
+
+## Risk & Correctness Issues
+[Present @check's issues verbatim, preserving its BLOCK/HIGH/MEDIUM/LOW
+severity and Must-fix/Follow-up OK priority labels.]
+
+## Simplification Opportunities
+[Present @simplify's findings verbatim, preserving its payoff/effort
+labels and category tags.]
+
+## Justified Complexity
+[@simplify's "Keep As-Is" items, if any]
+
+## What You Should Verify
+[@check's verification items]
+```
+
+---
+
+## Rules
+
+- Do NOT merge or normalize severity scales across agents. @check uses risk severity (BLOCK/HIGH/MEDIUM/LOW). @simplify uses payoff/effort. Show each in its native scale.
+- Do NOT invent your own issues. Only report what the agents found.
+- Do NOT add flattery, encouragement, or padding.
+- Do NOT deduplicate aggressively. If both agents flag the same location for different reasons, keep both -- the reader benefits from seeing both lenses.
+- The **Gate Verdict** (merge/no-merge decision) comes from @check only.
+- The **Simplification Recommendation** is advisory, not a merge gate.
+