✨ Teams Bot - Post an "SSW.Tiger is active" card into the meeting at start (needs custom bot)

Pain

The cleanest fix for end-of-meeting trigger confusion (#119) is a clear message shown inside the meeting the moment it starts, telling people Tiger is active and what to do at the end. Tiger's current pipeline has no meeting-start event, so this cannot be built today. It becomes possible once the custom Teams bot exists (the notification rework / custom Teams bot migration).

Split out from #119. The docs-and-notifications half ships in #127.

Blocked by

Custom Teams bot migration (the notification rework epic). This issue stays parked until that bot is registered and installed.

Feasibility (confirmed)

A custom Teams bot installed in a meeting receives a genuine meeting-start event via the Bot Framework SDK (OnTeamsMeetingStartAsync), provided its manifest carries the RSC permissions OnlineMeeting.ReadBasic.Chat (scheduled meetings) and ChannelMeeting.ReadBasic.Group (channel meetings). With the channel permission, the bot automatically receives start/end events for every channel meeting in teams where it is installed (exactly our sprint-review setup), so it does not need adding to each meeting individually. On that event the bot can post an Adaptive Card straight into the meeting chat.

Acceptance Criteria

1. When a monitored meeting starts, the bot posts a clear card into the meeting chat indicating SSW.Tiger is active.
2. The card explains the action required at the end to trigger the summary (stop recording or end the meeting).
3. The card states participants do NOT need to leave the meeting.
4. The card correctly states who receives the summary (consistent with the decision made in #127).
5. The card links to the Tiger documentation page (created in #127).
6. Wording is short, unambiguous, and suitable for non-technical users.

Notes

The docs page and recipient-behaviour decision both come from #127, so this issue reuses them rather than redefining them.

Start with the custom Teams bot migration and the Bot Framework OnTeamsMeetingStartAsync event, then read #127 for the documentation link and recipient decision. Done means a monitored meeting receives a short Adaptive Card stating Tiger is active, explaining the end action and that participants need not leave, with the correct recipient wording and documentation link.