feat: add typing-time autosuggest to slash commands

[honghua]

Replace the Tab-only readline completer with a prompt_toolkit PromptSession that renders an inline ghost suggestion while typing and a keyboard-selectable completion menu.
Fixes three user-visible defects in the REPL:

1. No as-you-type suggestion — completion only fired on Tab.
2. The popped-up match list was not selectable (no menu-complete binding, no arrow-key handling; the display hook was pure stdout.write).
3. Typing `/c` followed by more input dispatched as `/c/cwd` → "Unknown command", because `/` had been removed from readline's word delimiters and `handle_slash` splits only on whitespace.

Also surfaces modular/plugin/skill commands in completion for the first time. The previous completer read only the hand-maintained _CMD_META dict, while the dispatcher consulted the full live COMMANDS registry.

[chauncygu]

Thanks for the detailed PR! The autosuggest feature is a nice idea, but there are several issues that prevent merging as-is:

1. Hard dependency vs. fallback contradiction
   prompt_toolkit is added to dependencies (required), but ui/input.py has a HAS_PROMPT_TOOLKIT = False fallback path. Pick one — if it's required, the fallback is dead code; if it's optional,
   move it to [project.optional-dependencies].

2. History file format conflict
   readline and prompt_toolkit's FileHistory use different formats. Sharing the same HISTORY_FILE between them risks corrupting history, especially on fallback from prompt_toolkit to readline
   mid-session.

3. Circular import risk
   ui/input.py → import cheetahclaws → import ui.input creates a circular dependency. The lazy import mitigates it today, but it's fragile.

4. Multi-line paste behavior change
   The current _read_input has careful bracketed-paste handling (Phase 2/3) with a "pasted N lines" message. The prompt_toolkit path bypasses all of this, changing user-visible behavior
   silently.

5. Bug fix mixed with feature
   The readline /c/cwd glue fix and the prompt_toolkit feature should be separate PRs. We've already fixed the readline bug on main (changed "/" in line → line.startswith("/")).

If you'd like to revisit this, I'd suggest:

• Make prompt_toolkit an optional dependency
• Use a separate history file for prompt_toolkit
• Resolve the circular import (e.g. pass COMMANDS/META via setup() instead of importing cheetahclaws)
• Split the readline fix into its own PR

Thanks again for the contribution!

[honghua]

Thanks for the careful review — all five points addressed in the latest push.

[chauncygu]

Thanks for the thorough rework.

The PR looks good to merge, but main has changed significantly since your branch was created (module reorganization, config/runtime separation, new setup wizard, etc.), so there will be merge conflicts in cheetahclaws.py, pyproject.toml, and requirements.txt.

Could you rebase onto the latest main and resolve the conflicts? The changes are mostly mechanical — the key things to watch for:

• tools.py is now tools/init.py
• mcp/ is now cc_mcp/
• requirements.txt has been rewritten (core deps only, optional deps commented out)
• The REPL prompt now includes a context usage percentage indicator

Once rebased, I'll merge it.

Thanks a lot for your great contributions!

[honghua]

Rebased onto v3.05.70 — no merge conflicts after the mcp/ → cc_mcp/ rename and module reorg landed cleanly.

Also included a small CI-unblocking compat fix for tools/fs.py: three Path.read_text(newline=...) call sites were failing on Python 3.10–3.13 (the newline= kwarg on read_text is 3.14+ only). Swapped to open(..., newline="") via a small helper — same semantics, portable across all supported Python versions.

Happy to pull that fix into a separate PR if you'd prefer; it's a standalone 1-file, +14/-5 change. Full suite: 341/341 pass locally.

Ready for merge whenever you have a moment.

[chauncygu]

Thanks a lot!

Already merged.