Two fixes for /skills install and /skills uninstall slash commands:
1. input() hangs indefinitely inside prompt_toolkit's TUI event loop,
soft-locking the CLI. The user typing the slash command is already
implicit consent, so confirmation is now always skipped.
2. Cache invalidation was unconditional — installing or uninstalling a
skill mid-session silently broke the prompt cache, increasing costs.
The slash handler now defers cache invalidation by default (skill
takes effect next session). Pass --now to invalidate immediately,
with a message explaining the cost tradeoff. The CLI argparse path
(hermes skills install) is unaffected and still invalidates.
Fixes#3474
Salvaged from PR #3496 by dlkakbs.
82d6c28bd5