add Connectors & Setup Wizard page

Connectors.md

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+# Connectors & Setup Wizard
+
+`brain.py` is the engine. **Connectors + the setup wizard** are the product layer that turns it
+into a real "second brain" — plugging into the apps where your life actually lives, instead of
+manually pointing at directories.
+
+```
+   your apps ──▶ Connector ──▶ scrub() + _stage() ──▶ brain.db ──▶ recall
+ (mail, cloud,   (auth+pull)   (SAME engine path)                  (hybrid)
+  files, chat…)      │
+                     └── app credentials ──▶ encrypted vault  (NEVER in brain.db)
+```
+
+## Three-layer design (why it's built this way)
+1. **Engine** (`brain.py`) — pure, connector-agnostic, unchanged. Still usable as a bare library.
+2. **Connectors** — one per app. Each authenticates, pulls data, and feeds it through the engine's
+   **same scrub + dedup path** — so secrets inside emails/files are redacted before storage too.
+3. **Vault** (`connectors/vault.py`) — app logins are encrypted at rest (Fernet + PBKDF2, 390k
+   iters, `~/.secondbrain/vault.enc`, chmod 600). **`brain.db` never sees a credential.**
+
+This preserves SecondBrain's core promise — local-first, secrets-scrubbed — while adding real
+onboarding. (Verified: a `DB_PASSWORD=…` inside a synced file is scrubbed out of `brain.db`.)
+
+## The setup wizard
+```bash
+python3 setup.py          # pick apps → sign in → test connection → sync
+python3 setup.py sync     # re-sync all connected apps (cron/systemd timer)
+python3 setup.py list     # list available connectors
+```
+Set `BRAIN_VAULT_PASS` to run the `sync` non-interactively from a timer.
+
+## Connectors today
+| Connector | Auth | Ingests as |
+|---|---|---|
+| **Files & folders** | path | files |
+| **Email (IMAP)** | host + app password | events |
+| **Nextcloud / WebDAV** | URL + app password | files |
+
+## Roadmap connectors
+- **Google & Microsoft** (Gmail/Drive/Calendar, Outlook/OneDrive) — OAuth; needs the wizard's
+  local-web variant for the redirect + a registered app client id/secret.
+- **WhatsApp** (via Evolution API), **Calendar** (CalDAV), **Paperless-ngx**, **Odoo** (CRM/ERP),
+  **Obsidian** (vault folder), **Git/GitHub** (repos + issues).
+
+## Writing a connector (~40 lines)
+```python
+from .base import Connector, Field, register, feed
+
+@register
+class MyAppConnector(Connector):
+    id = "myapp"; name = "My App"; blurb = "Pull stuff from My App."
+    fields = [Field("host","Host"), Field("token","API token", secret=True)]
+    def test(self, cfg): ...            # verify creds, raise on failure
+    def sync(self, cfg):                # pull -> feed() -> engine scrub+stage
+        items = [{"text": "...", "ref": "...", "ts": "...", "project": "myapp"}]
+        return feed(items, "events")
+```
+Drop the file in `connectors/`; the wizard auto-discovers it. `feed()` runs everything through the
+engine's credential scrub — you never have to think about redaction.