refactor(browser): split installation and profile abstractions

A Chromium installation shares one master key across its profiles, but
modeling each profile as its own Browser re-derived the key per profile.
Browser now represents one installation holding its profiles and derives
the key once; new types.Profile/ExtractResult/CountResult carry per-profile
results.

cmd/hack-browser-data/keys.go

@@ -35,7 +35,7 @@ func keysExportCmd() *cobra.Command {
 		Example: `  hack-browser-data keys export -o dump.json
   hack-browser-data keys export -b chrome`,
 		RunE: func(cmd *cobra.Command, args []string) error {
-			browsers, err := browser.PickBrowsers(browser.PickOptions{
+			browsers, err := browser.DiscoverBrowsersWithKeys(browser.PickOptions{
 				Name:             browserName,
 				KeychainPassword: keychainPw,
 			})