Add activity strip and activity log to the admin member profile

[mroderick]

Summary

Last of the activity-log stack (base: #2854). Adds a GitHub-status-style weekly activity strip (52 ISO weeks, three states) plus a recent activity log on the admin member profile, rendered in the wide column. Both render for every member; not member-facing.

Fake data from local development shows what this could look like for someone very active.

Key changes

• Admin::Members::ActivityStrip service: one indexed query over activities owned by the member, bucketed into 52 ISO weeks; states :empty / :login_only (logins and logouts only) / :active (any other key); per-week key counts for tooltips.
• Admin::Members::ActivityStripComponent: 52 tall SVG bars, codebar blue for active weeks, with SVG <title> tooltips (ISO week + counts, e.g. "2026-W37 (week of 7 Sep 2026): 2 member login") and aria-label per bar; no JavaScript. Uses SVG titles rather than HTML title attributes so tooltips work in Firefox.
• Activity log: latest 30 activities for the viewed member, grouped under ISO week headings matching the strip's format, timestamps in Sunday, 2026-09-13 11:58 form. Each row links to the related entity where one exists — e.g. "Event invitation rsvp for " — with chapter-qualified group names ("Peterborough Coaches"); member-subject activities (logins, profile updates) render without links.
• Data fidelity: the log starts at instrumentation deploy (PR 1 of this stack) — earlier weeks read as empty by design.

Review notes

Week math and state classification live solely in the service (component renders only). Verified: full suite 1365/0, RuboCop clean.

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Context and motivation: #2857