docs(chat-apps): Slack & Teams usage guide (7 pages, usage-only)

[temalo]

What

Adds a new Chat Apps (Slack & Teams) documentation section — 7 pages covering how a user gets value from the CorpusIQ chat app once it's installed. Per the ask, this is usage only, not installation (install steps will change once the apps are in the Slack and Teams marketplaces).

Pages (docs/chat-apps/)

Page	Covers
README.md	Section index + the 3-step "short version"
what-it-is.md	What the app does, how it differs from the dashboard, the acts-as-you identity model, read-only framing
getting-started-slack.md	Link via /corpusiq-login, set your BYO AI key, ask your first question
getting-started-teams.md	Microsoft SSO variant of the same three steps
asking-questions.md	How to ask, what answers look like (tiles/cards), a starter prompt set by area
commands-and-account.md	/corpusiq-login, /corpusiq-logout, switching accounts
troubleshooting.md	The four things that block an answer: not linked, no AI key, tool not connected, wrong account (+ Teams sign-in)

The user-value flow it documents

Grounded in the real chat-apps surface behavior (I read the code, didn't invent the UX):

1. Link identity — the app won't read data until it knows who you are. Slack: /corpusiq-login → DM with link + code. Teams: Microsoft SSO. This is what makes it answer as you, from your connected tools.
2. Bring your AI key — prod is BYO-LLM; the user sets their own OpenAI/Anthropic/Azure OpenAI key in the dashboard. No key = the app says so rather than silently using someone else's.
3. Ask — DM or @-mention, plain English, answers render as Block Kit tiles (Slack) / Adaptive Cards (Teams).
4. Manage — /corpusiq-logout to unlink or switch accounts.

Voice & wiring

• Adam-class voice (plain, no slogans, banned-words discipline), matching the existing tree.
• <!-- screenshot: ... --> placeholders where a visual helps (no fabricated image URLs).
• Wired into mkdocs.yml nav as "Chat Apps (Slack & Teams)" after AI Integration.

Verification

• Local mkdocs build clean: all 7 pages render, section appears in nav, each page has a <meta name="description"> (152–202 chars). Zero "not found" nav warnings after placing files under the real docs_dir (docs/).
• Frontmatter validator passes on all 7 new files.
• Scrub grep clean — no internal refs (repo codenames, infra, team emails) leaked; support@corpusiq.io intentionally kept.

⚠️ Pre-existing CI note (not from this PR)

The repo-wide validate_frontmatter.py gate is currently red on 10 pre-existing broken files, all under docs/ SEO landing pages (docs/chatgpt-for-quickbooks.md, docs/claude-for-hubspot.md, docs/shopify-ai-analytics.md, etc.) — all failing invalid YAML frontmatter (line 2). I verified this breakage exists on untouched main (stashed my work, re-ran the validator → same 10). None of my files are among them. Per scope discipline I did not fold that repair into this PR; happy to open a separate fix PR for those 10 if you want. Flagging so the red check isn't mistaken for this change.

Hold for review

Public surface (corpusiq.io/docs) — not auto-merging. Handing you the URL for review. The screenshot placeholders are the one known gap: they need real Slack/Teams captures before this is fully polished for customers (a follow-up once we have a live workspace to capture from).