Task: portal balance widget — leaderboard mode

[avandenberghe]

Follow-up of avatharbe/bbAccounts-dev#83. Adds the second render mode envisioned in avatharbe/bbAccounts-dev#79 surface 4 (leaderboard) on top of the own-balance variant that shipped with avatharbe/bbAccounts-dev#83.

Scope

Per portal block instance, an admin chooses:

• the account_id whose balances to surface
• N (top-N members)

Block renders the top-N subledger balances on that account, descending by closing balance. Visible to all viewers; the data is whatever the admin chose to make public.

Per-instance config

bbGuild already has `bb_portal_config` for per-module-id key/value config. The leaderboard mode persists `account_id` and `top_n` there, edited via the bbGuild ACP portal screen's module-config form.

The own-balance mode (shipped) needs no config — keep it as the default. Adding leaderboard means the module's `get_template_acp()` returns a mode picker (own-balance / leaderboard) plus, when leaderboard is selected, an account_id dropdown and a top_n integer.

Files

• `portal/module/bbaccounts_balance.php` — extend `prepare_template()` to branch on the configured mode; add `get_template_acp()`
• New service method on `balance_summary` (or a sibling service) for top-N-on-account aggregation — keeps the SQL out of the portal module.
• `styles/prosilver/template/portal/bbaccounts_balance.html` — add a leaderboard-result branch
• `language/en/portal_bbaccounts.php` — heading, table headers, "configure account" prompt

Acceptance

• Mode selector visible in the bbGuild ACP portal block-config form.
• Leaderboard mode renders the top-N on the configured account.
• Anonymous viewers can see leaderboard data (the public mode); own-balance mode continues to require `u_accounts_view_own`.
• No new ledger service methods — top-N reuses existing per-account aggregate queries.

Notes

This was originally part of avatharbe/bbAccounts-dev#83's scope but the own-balance variant ships first because it's the higher-value path and adds zero ACP plumbing. Leaderboard adds the per-instance config story that bbGuild's portal supports but that avatharbe/bbAccounts-dev#83 didn't need.