fix: resolve active Chromium profile for browser history import

[vingeraycn]

Problem

All Chromium-family browsers hardcode Default/History as the history file path in listImportableBrowsers(). Users with non-default Chrome profiles (e.g. 'Profile 7') cannot import their browser history — the browser shows as unavailable in the import dropdown.

Fixes #401

Solution

Added resolveChromiumHistoryPath(rootDir) which dynamically resolves the correct profile directory:

1. Local State — Reads {rootDir}/Local State JSON to find profile.last_used (the active profile)
2. Default fallback — If Local State is missing or the profile has no History file, falls back to Default/History
3. Profile scan — If Default doesn't exist either, scans all Profile * and Default subdirectories, returning the first with a History file
4. Last resort — Returns Default/History path even if it doesn't exist (caller checks existence)

Changes

• Added resolveChromiumHistoryPath() helper with the 4-tier resolution algorithm
• Changed Chromium browser definitions from hardcoded dbPath to rootDir
• Display name includes profile name when not 'Default' (e.g., 'Google Chrome (Profile 7)')
• No changes to ImportableBrowser interface — fully backward compatible
• No changes to importFromBrowser() signature — existing callers unaffected

Testing

• TypeScript compilation passes (tsc --noEmit)
• Main build passes (npm run build:main)
• Manually verified that Chrome with 'Profile 7' is now correctly detected