feat(teams): add Microsoft Teams platform adapter as a plugin

Hello! I am the maintainer of the microsoft-teams-apps Python SDK and
I built this Teams adapter to integrate Microsoft Teams into Hermes.

Adds a `plugins/platforms/teams` platform plugin using the new
PlatformRegistry system from #17751. The adapter self-registers via
`register(ctx)` — no hardcoding in run.py, toolsets.py, or any
other core file.

Key features:
- Supports personal DMs, group chats, and channel posts
- Adaptive Card approval prompts with in-place button replacement
  (Allow Once / Allow Session / Always Allow / Deny)
- aiohttp webhook server bridged from the Teams SDK to avoid
  the fastapi/uvicorn dependency
- ConversationReference caching for correct proactive sends in
  non-DM chats
- `interactive_setup()` for `hermes gateway setup` integration
- `platform_hint` for LLM context (Teams markdown subset)
- 34 tests covering adapter init, send, message handling, and
  plugin registration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -398,3 +398,19 @@ IMAGE_TOOLS_DEBUG=false
 # Override STT provider endpoints (for proxies or self-hosted instances)
 # GROQ_BASE_URL=https://api.groq.com/openai/v1
 # STT_OPENAI_BASE_URL=https://api.openai.com/v1
+
+# =============================================================================
+# MICROSOFT TEAMS INTEGRATION
+# =============================================================================
+# Register a Bot in Azure: https://dev.botframework.com/ → "Register a bot"
+# Or use Azure Portal: Azure Active Directory → App registrations → New registration
+# Then add the bot to Teams via the Bot Framework or App Studio.
+#
+# TEAMS_CLIENT_ID=                     # Azure AD App (client) ID
+# TEAMS_CLIENT_SECRET=                 # Azure AD client secret value
+# TEAMS_TENANT_ID=                     # Azure AD tenant ID (or "common" for multi-tenant)
+# TEAMS_ALLOWED_USERS=                 # Comma-separated AAD object IDs or UPNs
+# TEAMS_ALLOW_ALL_USERS=false          # Set true to skip the allowlist
+# TEAMS_HOME_CHANNEL=                  # Default channel/chat ID for cron delivery
+# TEAMS_HOME_CHANNEL_NAME=             # Display name for the home channel
+# TEAMS_PORT=3978                      # Webhook listen port (Bot Framework default)