Document multi-agent ticket claiming convention

[0xLeif]

Summary

Docs-only: reconciles the two parallel agent ticket-claiming sections (PR #2's "Agent ticket claims" and this PR's original draft) into one Multi-agent ticket claiming section in AGENTS.md, and adds a Worktrees for parallel agents subsection. Everything lives outside the managed trust block.

The merged convention, live in repo labels (agent:kimi, agent:cursor):

• Check labels and linked PRs before starting; skip claimed tickets
• Claim with your agent:<name> label plus a comment naming your working branch
• One agent per ticket, one ticket per branch/PR
• Remove the label and link the outcome when the PR is up or work stops
• Parallel local agents use per-ticket git worktrees outside the main checkout

SpecSync

• CHG-0006 (documentation, no-spec) accepted for this change
• CHG-0005 evidence rebound via audited reopen (AGENTS.md input changed after its acceptance)

Verification

• fledge lanes run verify green (build + test + smoke)
• specsync check --force green (6/6 files, 100%)
• specsync change check: 5 active changes valid, CHG-0005 and CHG-0006 evidence exact
• Managed block markers untouched (trust CI greps for them)

[cursor]

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