feat: --issue flag to fetch and inject GitHub issue body into agent prompt

[marshall-ch-personal]

Problem

When the AIPMO pipeline dispatches a coding agent for a GitHub issue, the issue body (which contains the full spec, acceptance criteria, library names, etc.) gets summarized/rephrased by the supervisor SOP before reaching the coding agent. This telephone game loses critical details.

Proposed Solution

Add --issue <number> flag to agentctl launch. When provided:

1. Fetch the issue via gh issue view <number> -R <repo> --json title,body,labels
2. Inject the full issue title + body into the agent prompt as context (similar to --spec)
3. Optionally accept --repo <owner/repo> to specify which repo (default: infer from CWD)

Example

agentctl launch claude-code \
  --worktree ~/personal/template \
  --branch feat/12-tauri-desktop \
  --issue 12 \
  -p 'Implement this issue. Follow the spec exactly.'

The agent would receive:

--- GitHub Issue #12: Spike: Add Tauri desktop app stack with E2E testing ---
[full issue body here]
---
Implement this issue. Follow the spec exactly.

Why This Matters

Today we lost 2+ hours because three coding agents all ignored the core requirement (integrate a specific library) because the supervisor rephrased the issue instead of passing it verbatim. The issue body was perfectly clear — the telephone game broke it.

Workaround

SOPs can do this manually:

gh issue view 12 -R c-h-personal/template --json body --jq .body > /tmp/issue-12.md
agentctl launch claude-code --spec /tmp/issue-12.md -p 'Implement this issue.'

But --issue would make this first-class and ensure it always happens.