Epic detection and setup in `il start`

[acreeger]

Summary

Add epic detection logic to the il start command: detect the iloom-epic label, confirm swarm mode with the user, create an epic loom with its own integration branch, and handle the --swarm and --max-agents CLI flags.

Context

Part of the Autonomous Swarm Mode epic (#557). This issue handles the entry point UX — detecting that a user is starting an epic (not a regular issue) and setting up the epic-level infrastructure before the supervisor takes over.

Scope

Epic Detection

In StartCommand (after fetching the issue), check:

1. Issue has iloom-epic label
2. Issue has child issues (via getChildIssues())
3. Child issues have dependencies (via getDependencies())

If all conditions met → epic mode. If label present but no children → warn and proceed as normal issue.

Confirmation Prompt

Show interactive confirmation:

Issue #42 is an epic with 8 child issues (5 ready, 3 blocked).
Start swarm mode? Max 3 concurrent agents. [Y/n]

• Interactive: show prompt, respect answer
• Non-interactive (no TTY): skip (require --swarm flag)
• --swarm flag: bypass confirmation, start swarm immediately
• --swarm on non-epic: silently ignored, proceed as normal il start

CLI Flags

Add to il start in cli.ts:

• --swarm — bypass epic confirmation, auto-confirm swarm mode
• --max-agents <n> — override swarm.maxConcurrent setting for this run

Epic Loom Creation

When entering swarm mode, create an epic-level loom:

• Branch name: standard naming (e.g., issue-42-swarm-mode)
• This branch serves as the integration branch — all child PRs target it
• Uses standard LoomManager.createIloom() with enableClaude: false, enableCode: false, enableDevServer: false, enableTerminal: false
• Epic loom metadata should include { isEpic: true, swarmStatus: 'pending' }

Edge Cases

• Epic with 0 child issues → warn, skip swarm, proceed as normal issue
• Epic with children but no dependencies → warn that all tasks will run in parallel
• Issue without iloom-epic label but with child issues → normal issue (no auto-swarm)
• Already have an active epic loom for this issue → offer to resume

Acceptance Criteria

• il start <epic-number> correctly detects iloom-epic label
• Interactive confirmation prompt shows child issue summary
• --swarm flag bypasses confirmation
• --swarm on non-epic is silently ignored
• --max-agents override works
• Epic loom created with integration branch
• Edge cases handled gracefully (0 children, no deps, existing loom)
• Unit tests cover detection logic and CLI flag handling

Scope Boundaries

• Does NOT launch the supervisor loop (that's wired in Claude CLI Integration #12/wire issue)
• Does NOT create child worktrees (supervisor handles that)

Dependencies

• Beads integration, settings, sync, and epic label #558 (Beads integration) — needs BeadsManager for child issue / dependency queries