feat: show who an Azure account signs in as, in Details on its row (#5)

On an Azure account's group row, the Details pane now describes the account:

| field | from |
|---|---|
| name | token `name` |
| user (and "service principal") | az's account list |
| tenant: name · ID | az's account list (the name is borrowed from another entry in the same tenant when az left it out) |
| object ID | token `oid`; `y` on the row copies it |
| sign-in: MFA or not, and how | token `amr` |
| directory roles | token `wids`: built-in roles by name, others as `role 1a2b3c4d`, the default member role left out |
| subs: count · default | az's account list |
| cloud | az's account list, when not AzureCloud |

Nothing is fetched for it: the claims are the ones from the token lazysecrets already gets for the account's own tenant, read without verification. The token itself is never stored or shown. Before the first token, only the az-list fields show. A failing account shows its sign-in problem there instead (from #4).

New optional `provider.Accounts` interface; `azure.Provider` implements it. Tests: the fields from claims and az's list, sign-in methods, the UI showing it on the group row only, and `y` copying the object ID. Checked against a real signed-in account (name, MFA · password, default subscription) and an expired one (az-list fields only, since there's no token).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>
Reviewed-on: #5

internal/provider/azure/cli.go

@@ -42,6 +42,16 @@ type cliCredential struct {
 
 	mu    sync.Mutex
 	cache map[string]azcore.AccessToken // by resource and tenant argument
+	// last is the claims of the latest token in the account's own
+	// tenant, to describe the account (Provider.Account).
+	last map[string]any
+}
+
+// claims are the latest token's claims, nil before the first.
+func (c *cliCredential) claims() map[string]any {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.last
 }
 
 func newCLICredential(user, tenant string, accounts func() ([]account, error)) *cliCredential {
@@ -110,29 +120,38 @@ func (c *cliCredential) GetToken(ctx context.Context, opts policy.TokenRequestOp
 	if err != nil {
 		return azcore.AccessToken{}, err
 	}
-	if u, ok := tokenUser(tok.Token, others); ok {
+	claims := tokenClaims(tok.Token)
+	if u, ok := tokenUser(claims, others); ok {
 		return azcore.AccessToken{}, fmt.Errorf("az gave a token for %s, not %s: sign in as %s again", u, c.user, c.user)
 	}
+	if !otherTenant && claims != nil {
+		c.last = claims
+	}
 	c.cache[key] = tok
 	return tok, nil
 }
 
-// tokenUser reports which of users a token was issued to, if any, from
-// its claims. The token isn't verified: this only catches az picking the
-// wrong signed-in account.
-func tokenUser(token string, users []string) (string, bool) {
+// tokenClaims reads a JWT's claims, without verifying it: they only
+// describe the account and catch az picking the wrong one. nil if it
+// isn't a JWT.
+func tokenClaims(token string) map[string]any {
 	parts := strings.Split(token, ".")
-	if len(parts) != 3 || len(users) == 0 {
-		return "", false
+	if len(parts) != 3 {
+		return nil
 	}
 	b, err := base64.RawURLEncoding.DecodeString(strings.TrimRight(parts[1], "="))
 	if err != nil {
-		return "", false
+		return nil
 	}
 	var claims map[string]any
 	if json.Unmarshal(b, &claims) != nil {
-		return "", false
+		return nil
 	}
+	return claims
+}
+
+// tokenUser reports which of users a token's claims are for, if any.
+func tokenUser(claims map[string]any, users []string) (string, bool) {
 	for _, name := range []string{"upn", "unique_name", "preferred_username", "email"} {
 		v, _ := claims[name].(string)
 		if i := strings.LastIndexByte(v, '#'); i >= 0 {