feat(adapters/msteams): land Microsoft Teams adapter as experimental (needs live-tenant validation)

[ThomasK33]

Track landing the Microsoft Teams adapter (adapters/msteams) at the experimental tier, per ADR 0007.

Status

A high-quality spike exists as draft PR #4: self-contained (zero core-runtime changes, zero new dependencies), stdlib-only Bot Framework JWT/JWKS verification, versioned opaque thread IDs carrying conversationReference, reuse of internal/ratelimit and the Observer hooks, ~78% statement coverage against a mocked Bot Framework server.

The spike resolved ADR 0007 open question 9 (no msbotbuilder-go; hand-rolled stdlib JWT validation works, no new deps). The remaining 9 of 10 open questions require a live Azure Bot registration + Teams tenant to validate (ack/turn semantics, endorsement behavior on production keys, markdown fidelity, serviceUrl/conversation-id stability, proactive posting prerequisites, aadObjectId stability, etc.). See the 10-point checklist in PR #4.

Path to land

1. A human with Azure Bot + Teams tenant access runs the live validation checklist from PR Spike: Microsoft Teams Adapter (Bot Framework) (ADR 0007) #4.
2. Update ADR 0007 → Accepted, recording confirmed findings.
3. Mark the package experimental in adapters/msteams/doc.go (honest tier labeling).
4. Undraft PR Spike: Microsoft Teams Adapter (Bot Framework) (ADR 0007) #4, pass CI + @codex review + @codex security review, merge.

Blocked on: live-tenant access (human).

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