Standardize session-list tables on one canonical row builder

[KucharczykL]

Summary

Sessions are rendered by three different table layouts that have drifted apart. They should share one canonical row builder. Canonical target: the list_sessions 6-column table.

Current state

Where	Columns	How rows are built
games/views/session.py list_sessions	6: Name, Date, Duration, Device, Created, Actions	row dict with row_id + hx attrs → TableRow
games/views/game.py _sessions_section (game detail)	4: Game, Date, Duration, Actions	plain list, no row_id, no Device column
games/views/session.py _session_row_fragment	4: Name, Start, End, Duration	hand-built Tr, no row_id

Each is maintained independently, so a change to the session row (new column, formatting, action button) has to be made in up to three places and silently drifts otherwise. This is the root cause of #53.

Desired state

• One canonical row builder (extracted from list_sessions, e.g. session_row_data(session, device_list, csrf_token)) used everywhere a session row is rendered.
• The game-detail sessions table migrates onto it (dropping/adapting columns as needed for that context, e.g. it may hide Device/Created but should not re-implement the row).
• No hand-rolled session <tr> anywhere.

Notes

• Stale _session_row_fragment no longer matches the live session list table #53 introduces session_row_data for the list + htmx fragment. This issue tracks finishing the job by also moving the game-detail table onto it.
• The game-detail table uses Game as the first column vs Name and omits Device/Created — standardization needs a way to vary visible columns from one row source.