fix(workspace): bound worktree add admission

[chubes4]

Summary

• cap repository-preflight and global-capacity lock admission at 30 seconds
• recompute the second admission wait from the shared aggregate operation deadline
• return typed retryable timeout evidence with request, queue, owner, ETA, retry command, and no-mutation state
• add deterministic deadline/cap and contention diagnostics without real sleeps or source-shape assertions

Addresses #1132.

This bounds silent lock admission before normal caller timeouts. The synchronous CLI still emits its typed result when the bounded wait expires rather than streaming progress during the wait.

Verification

• php -l inc/Workspace/WorkspaceWorktreeLifecycle.php
• php -l tests/worktree-add-aggregate-deadline.php
• php tests/worktree-add-aggregate-deadline.php
• php tests/workspace-capacity-lock-concurrency.php
• php tests/worktree-add-cli-output-budget.php
• composer validate --no-check-publish
• git diff --check

AI assistance

OpenAI GPT-5.6 Sol via OpenCode traced the duplicated admission budget, implemented bounded shared-deadline waits and typed diagnostics, replaced a source-shape assertion with behavioral coverage, reviewed the diff, and ran verification. Chris Huber is responsible for every line.