bug: wt hook pre-start uses FailFast instead of Warn #1703

Bug

wt hook pre-start uses HookFailureStrategy::FailFast (aborts on failure), but execute_pre_start_commands during automatic worktree creation uses HookFailureStrategy::Warn (warns and continues).

The documentation in wt hook --help explicitly says:

failure aborts the operation (except pre-start, which warns and continues)

Reproduction

# Configure a pre-start hook that fails
wt config create --hooks.pre-start='["false"]'

# Manual invocation aborts (bug — should warn and continue)
wt hook pre-start  # exits non-zero

# Automatic invocation during create warns and continues (correct)
wt switch --create test-branch

Root Cause

In src/commands/hook_commands.rs:265, HookType::PreStart is grouped with PreSwitch, PreRemove, PreCommit, and PreMerge in the FailFast match arm. It should have its own match arm using HookFailureStrategy::Warn, matching the behavior in src/commands/worktree/hooks.rs:28.

Fix

Separate PreStart from the FailFast group and give it Warn strategy.