Add repository traffic/insights tools (views, clones, referrers, paths)

[musch711]

Closes #3164.

Adds four read-only tools under the repos toolset that wrap GitHub's repository traffic endpoints:

Tool	Endpoint
get_traffic_views	GET /repos/{owner}/{repo}/traffic/views
get_traffic_clones	GET /repos/{owner}/{repo}/traffic/clones
get_traffic_referrers	GET /repos/{owner}/{repo}/traffic/popular/referrers
get_traffic_paths	GET /repos/{owner}/{repo}/traffic/popular/paths

Why

Agents can already read stars and forks but have no view into whether a repo is actually being visited or cloned, which is the primary signal for adoption and reach. Because GitHub only retains traffic data for a rolling 14-day window, an agent that snapshots it on a schedule is the natural use case for longer-term trend tracking.

Implementation notes

• All four are ReadOnlyHint: true under the existing repos toolset.
• The pinned go-github v89 client already exposes ListTrafficViews, ListTrafficClones, ListTrafficReferrers, and ListTrafficPaths, so there is no new HTTP plumbing. views/clones take an optional per (day|week) mapping to TrafficBreakdownOptions; referrers/paths take just owner/repo.
• These endpoints require push access (GitHub App: Administration: Read), so the tools use scopes.RequireAll(scopes.Repo) rather than public-read.
• Traffic data is never world-readable, so results carry a new static IFC label LabelRepoTraffic() (always private, mirroring LabelCollaboratorRoster).
• Added tests (success + no-push-access 403) for each tool, regenerated tool snapshots, and regenerated docs.