Feature request: trigger slash command palette at any caret position, not only at input start

[ffftttft]

Problem

The slash command palette only opens when the entire input starts with / and contains no whitespace:

• Palette query: value.startsWith("/") && !/\s/.test(value.slice(1)) in components/ChatInput.tsx
• Built-in command dispatch also only fires when the message starts with /

This means you can't describe your task first and then attach a skill. In Codex CLI / Claude Code, a common flow is:

refactor the auth module to use refresh tokens /my-skill

…where typing / after a space (or anywhere at the caret) opens the skill palette, and selecting a skill inserts the command at the caret. In pi-web today that flow is impossible — you have to open the palette first, before typing anything.

Proposal

Make the slash trigger caret-based, mirroring how the @ file autocomplete already works in the same component ("recomputed from the text before the caret on every change/caret move"):

1. Detect a / token at the caret — i.e. / at position 0, or preceded by whitespace, and the token up to the caret contains no whitespace.
2. Open the palette anchored to that token; filter as the user keeps typing within the token.
3. On select, replace only the /query token at the caret with the chosen command, preserving the surrounding text.
4. Keep the existing start-of-input behavior unchanged (it becomes a special case of the above).

Open question: should built-in command dispatch (onBuiltinCommand) also accept mid-message /command, or stay start-of-message only? I'd lean toward keeping dispatch as-is (start only) and only widening the palette trigger — inserting a skill mid-text expands to text the model sees, which matches CLI behavior.

Notes

• Happy to contribute a PR for this.
• Heads-up: open PR feat: group dormant skills in skills panel and slash palette #288 also touches the slash palette in ChatInput.tsx (rendering side). This change is about trigger logic, so overlap should be small — I'll rebase if it lands first.