[FEATURE] Include teammate sessionId in Agent Teams config.json for session→transcript mapping

Request

Add each teammate's own sessionId (the JSONL UUID) to its member entry in ~/.claude/teams/<team>/config.json.

Problem

External tools that monitor Agent Teams can identify a teammate and its lead, but cannot reach the teammate's transcript, because:

• The config member entry has agentId (name@team) but no sessionId.
• The teammate process does receive --agent-id and --parent-session-id on argv — so the harness clearly knows the mapping at spawn — but never writes a ~/.claude/sessions/<pid>.json the way a lead does.
• Result: there is no on-disk bridge from a member to its JSONL. The only workaround is scanning every top-level JSONL's first record for teamName/agentName, which is O(files) per refresh and races with rotation.

Proposed change

Include sessionId in each member entry (the UUID already exists — it names the JSONL). That's the whole fix.

Prior art

• #41186 raised this (problem #2) plus related manifest gaps; it was auto-closed NOT_PLANNED for inactivity, not on merits — reopening the specific, cheapest piece.
• #7881 (open) is the same identification gap on the hooks surface.