[FEATURE] Allow customizing auto-generated conversation tab titles (length / format)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Summary

Conversation tabs in the VS Code extension are auto-titled based on the first user message. There is currently no way to influence how these titles are generated, and they are often quite long, which clutters the tab bar when several sessions are open in parallel.

Use case

I keep many parallel Claude Code sessions open in VS Code (often 5–10 at a time across different small tasks). Long auto-titles like "Strato deploy investigation for unshipped title changes" make the tab strip unreadable and force horizontal scrolling. I would prefer very short titles (1–2 words / ~10 characters) so I can scan tabs at a glance.

Manual rename works but is friction for short-lived sessions.

Proposed options (any of these would help)

1. A settings.json field, e.g.:

```json
{
"conversationTitle": {
"maxLength": 20,
"maxWords": 2
}
}

1. A custom prompt override for the title-generation step (e.g. "conversationTitlePrompt": "Summarize in max 2 words, max 10 characters.").
2. A hook (e.g. SessionTitle) that lets the user post-process the generated title.
3. A slash command like /title <name> to set the current tab's title without going through hover + rename.

Environment
Claude Code in VS Code extension Antigravity
Windows 11
Thanks!

Proposed Solution

Proposed options (any of these would help)

1. A settings.json field, e.g.:

```json
{
"conversationTitle": {
"maxLength": 20,
"maxWords": 2
}
}

1. A custom prompt override for the title-generation step (e.g. "conversationTitlePrompt": "Summarize in max 2 words, max 10 characters.").
2. A hook (e.g. SessionTitle) that lets the user post-process the generated title.
3. A slash command like /title <name> to set the current tab's title without going through hover + rename.

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_