docs: add wiki and refresh flat lib with mcp artifacts

- Add hand-written wiki (index, overview, how-to, extending, dev)
  following the platform anatomy
- Remove stale nested docs/lib/mail_intake and regenerate the flat
  lib reference to match docforge.nav.yml
- Regenerate MCP bundle with standardized docstrings

docs/wiki/01_overview.md

@@ -0,0 +1,91 @@
+# 🧱 Overview
+
+Mail Intake is a **contract-first ingestion pipeline**. Adapters handle
+transport to a provider, parsers normalize provider payloads, and the reader
+orchestrates the whole flow into canonical domain models.
+
+---
+
+## 🏗️ Architecture
+
+```text
+                 ┌─────────────────────────────────────────┐
+                 │  External Provider (e.g. Gmail API)     │
+                 └─────────────────────┬───────────────────┘
+                                      │
+                    ┌─────────────────▼──────────────────┐
+                    │  MailIntakeAdapter (transport)      │   provider API calls
+                    └─────────────────┬──────────────────┘
+                                      │  provider-native payloads
+                    ┌─────────────────▼──────────────────┐
+                    │  Parsers (normalization)           │   headers, body, subject
+                    └─────────────────┬──────────────────┘
+                                      │  composed
+                    ┌─────────────────▼──────────────────┐
+                    │  MailIntakeReader (orchestration)  │   iter_messages / iter_threads
+                    └─────────────────┬──────────────────┘
+                                      │
+                    ┌─────────────────▼──────────────────┐
+                    │  MailIntakeMessage / Thread        │   canonical domain models
+                    └────────────────────────────────────┘
+```
+
+Layers:
+
+1. **Adapters** (`mail_intake.adapters`) — provider-specific, read-only
+   transport. Return provider-native payloads; never interpret them.
+2. **Auth** (`mail_intake.auth`) — credential acquisition and lifecycle
+   management, decoupled from adapters.
+3. **Credentials** (`mail_intake.credentials`) — persistence of auth tokens;
+   `PickleCredentialStore` locally, `RedisCredentialStore` for production.
+4. **Parsers** (`mail_intake.parsers`) — extract headers, body text, sender,
+   and normalized subjects from provider payloads.
+5. **Ingestion** (`mail_intake.ingestion`) — `MailIntakeReader` wires an
+   adapter + parsers into iterators over canonical models.
+6. **Models** (`mail_intake.models`) — provider-agnostic `MailIntakeMessage`
+   and `MailIntakeThread`.
+
+---
+
+## 📦 Domain models
+
+`MailIntakeMessage`:
+
+| Field | Type | Meaning |
+|---|---|---|
+| `message_id` | `str` | Provider message id |
+| `thread_id` | `str` | Conversation thread id |
+| `timestamp` | `datetime` | Message timestamp |
+| `from_email` | `str` | Sender email |
+| `from_name` | `str \| None` | Sender display name |
+| `subject` | `str` | Message subject |
+| `body_text` | `str` | Extracted plain-text body |
+| `snippet` | `str` | Provider snippet |
+| `raw_headers` | `dict[str, str]` | Unmodified headers |
+
+`MailIntakeThread`:
+
+| Field | Type | Meaning |
+|---|---|---|
+| `thread_id` | `str` | Conversation id |
+| `normalized_subject` | `str` | Normalized subject (threads share one) |
+| `participants` | `set[str]` | Distinct senders |
+| `messages` | `list[MailIntakeMessage]` | Ordered messages |
+| `last_activity_at` | `datetime \| None` | Latest message time |
+
+---
+
+## 🔒 Design guarantees
+
+- Read-only access — no mutation of provider state.
+- Provider-agnostic domain models.
+- Explicit configuration and dependency injection (no implicit env reads).
+- Extensible via public contracts; built-in adapters are reference
+  implementations and may change internally.
+
+---
+
+## 📚 Read Next
+
+- [How to Use](02_how_to_use.md) — the Gmail ingestion flow.
+- [Extending Mail Intake](03_extending.md) — custom adapters and stores.