fix: preserve user's browser tabs on connect and newChat

[itsbrex]

Problem

comet_connect and comet_ask (with newChat: true) call a "close all tabs except one" cleanup on every startup/reset:

// Close extra tabs, keep only one
if (pageTabs.length > 1) {
  for (let i = 1; i < pageTabs.length; i++) {
    try { await cometClient.closeTab(pageTabs[i].id); } catch {}
  }
}

For anyone who keeps Comet open as their normal browser, this silently destroys their session — in my case Connected to Perplexity (cleaned 105 old tabs) on first connect. Losing 100+ tabs to an MCP connect is a nasty surprise.

Fix

Stop closing tabs. Instead:

• comet_connect — reuse the existing Perplexity tab via listTabsCategorized() (tabs.main). If there isn't one, open a single new tab. Other tabs are never touched.
• comet_ask (newChat) — same reuse-or-open logic, no cleanup loop.

This also avoids hijacking an arbitrary tab: rather than connecting to "the first page tab" and navigating it to Perplexity, it targets the actual Perplexity tab (tabs.main) and only creates a new tab when none exists.

Notes

• No new dependencies, no API changes. Connect message now reports tabs preserved instead of tabs cleaned.
• Related: Stop closing user's existing browser tabs on connect #2 takes a similar "don't close tabs" direction; this PR additionally reuses the existing Perplexity tab (via listTabsCategorized) instead of navigating the first available tab, so an unrelated foreground tab isn't repurposed.
• tsc compiles clean.