GeezerVison

Adds the project summaries endpoint and pin telemetry on top of #32025. The Projects page grid and the sidebar's pinned projects both read these summaries.

• GET /api/experimental/chats/projects/summaries returns a ChatProjectSummary for every project in the existing project list (same set, same permissions): pinned, pin_order, own_chat_count, own_unread_count, own_running, own_needs_attention (requires_action, error or paused), last_activity_at (newest updated_at among the caller's counted chats) and member_count. Counts use only the caller's own top-level, non-archived chats; unread uses the same rule as has_unread. It is one grouped query.
• Member count is the distinct non-deleted, non-system users who can use the project: the owner, user_acl users who are in the project's org, and members of group_acl groups (including Everyone). It is 1 when chat sharing is disabled or the chat-project-sharing experiment is off.
• Visibility vs. member counting: which projects and pins are visible follows RBAC (grants count unless chat sharing is disabled), so summaries always match GET /chats/projects. Only member_count also depends on the experiment.
• Telemetry: a ChatProjectPins snapshot with active pins and tombstones by source, users with projects and with tombstones, and two histograms of the share of projects users have pinned (all users, and users who have acted on pins). No user, project or organization identifiers.

The existing GET /api/experimental/chats/projects is unchanged.

{"name":"Alpha","pinned":true,"pin_order":1,"own_chat_count":0,"own_unread_count":0,"own_running":false,"own_needs_attention":false,"last_activity_at":null,"member_count":1}
{"name":"Bshared","pinned":false,"pin_order":0,"own_chat_count":0,"own_unread_count":0,"own_running":false,"own_needs_attention":false,"last_activity_at":null,"member_count":2}