Add bounded consumer subscription expression portfolio

## Problem

Subscription details are currently loaded one consumer group at a time. Operators cannot audit expression styles, filter modes, or consistency across an instance, and a fleet-wide manual review can generate an uncontrolled number of requests.

## Proposed change

Add an on-demand subscription portfolio that:

- loads all matching consumer groups through the existing bounded pagination helper;
- inspects at most 100 groups with four concurrent subscription requests;
- isolates per-group failures and reports explicit coverage and omissions;
- classifies wildcard, tag-set, SQL, empty, and other expressions;
- aggregates filter mode, type, consistency, groups, topics, and representative expressions;
- supports attention filtering and search with Chinese/English copy and focused tests.

This is a read-only workflow over existing consumer-group and subscription endpoints.

Start with the existing bounded pagination helper and the consumer-group and subscription endpoints described in the issue. Trace how the dashboard loads and presents subscription details, then verify that the portfolio limits groups and concurrency, isolates failures, reports coverage and omissions, classifies and aggregates expressions, and supports attention filtering, search, Chinese/English copy, and focused tests.

Written by the indexing model from the issue text.