fix(tui): 修正 Bash Ctrl+B 提示计时

[cc-claws]

Fixes #111

Summary

• record the real streaming shell spawn time in ShellExecution
• keep Bash ToolBlock timer unset at ToolStart and fill it when the agent shell registration arrives
• add regression tests for pending Bash timer behavior

Validation

• cargo test -p peri-tui --lib test_bash_tool_start_uses_spawn_started_at
• cargo test -p peri-tui --lib test_set_pending_bash_tool_started_at_in_view
• git diff --check
• workflow_dispatch CI run 28572326249 passed on ubuntu, macOS, and Windows

Note: local cargo check -p peri-tui could not complete because D: had only 0.14GB free and rustc failed with os error 112.