Build the governance module scaffold behind its feature flag

[Lakes41]

Difficulty: Advanced | Type: Feature

Background: NEXT_PUBLIC_FEATURE_GOVERNANCE exists, defaulting to false everywhere, and "governance" is listed as not yet built, paralleling the "Advanced governance permissions" deferred area on the guildpass-core backend.

Problem: Like analytics, there is no implementation behind this flag yet — communities that want basic governance visibility (e.g. viewing role hierarchies, pending admin actions) have nothing to look at even when the flag is enabled.

Expected Outcome: An initial governance module renders a read-only view of the community's current roles, role assignments, and any admin-configured access policies in one consolidated dashboard, laying groundwork for future write actions.

Suggested Implementation: Add app/admin/governance/ gated by the flag, aggregating existing GET /v1/members (for role distribution) and GET /v1/policies data into a single governance-overview page, explicitly scoped as read-only for this first iteration with a documented note on what's intentionally out of scope.

Acceptance Criteria:

• Governance page renders correctly gated by its flag, hidden by default.
• Shows accurate role distribution and policy overview from existing data sources.
• PR description or in-code comment clearly scopes this as read-only v1, listing deferred write-capabilities for follow-up issues.

Likely Affected Files/Directories: app/admin/governance/ (new), lib/features.ts, components/nav.tsx

Labels: feature, architecture, GrantFox OSS, Maybe Rewarded, Official Campaign | FWC26