docs: idiomatic Elixir and Phoenix patterns with verified source citations

Extracted patterns from Elixir core and Phoenix source code with specific
file:line citations, then verified all citations against the actual source
in a second pass.

Structure:
- patterns/ — Elixir core patterns (GenServer, errors, data, types, etc.)
- phoenix/ — Phoenix-specific patterns and deviations
- comparison/ — Elixir vs Phoenix side-by-side
- smells/ — Anti-patterns and common mistakes
- changelog/ — Daily Elixir/Phoenix PR digest (auto-updated)

phoenix/deviations.md

@@ -10,7 +10,7 @@ Where Phoenix deliberately differs from Elixir core patterns and why.
 
 **Phoenix deviation:** The Router uses macros extensively.
 
-**Source:** `lib/phoenix/router.ex:109-123`
+**Source:** `lib/phoenix/router.ex:106-128`
 
 > We use `get`, `post`, `put`, and `delete` to define your routes. We use macros
 > for two purposes:
@@ -31,10 +31,12 @@ Where Phoenix deliberately differs from Elixir core patterns and why.
 
 **Phoenix deviation:** The Router imports entire modules:
 
-**Source:** `lib/phoenix/router.ex:274-276`
+**Source:** `lib/phoenix/router.ex:303-306`
 
 ```elixir
 import Phoenix.Router
+
+# TODO v2: No longer automatically import dependencies
 import Plug.Conn
 import Phoenix.Controller
 ```
@@ -49,13 +51,24 @@ import Phoenix.Controller
 
 **Phoenix deviation:** Aggressive use of module attribute accumulation.
 
-**Source:** `lib/phoenix/router.ex:271-280`
+**Source:** `lib/phoenix/router.ex:297-312`
 
 ```elixir
-Module.register_attribute(__MODULE__, :phoenix_routes, accumulate: true)
-@phoenix_pipeline nil
-Phoenix.Router.Scope.init(__MODULE__)
-@before_compile unquote(__MODULE__)
+defp prelude(opts) do
+  quote do
+    Module.register_attribute(__MODULE__, :phoenix_routes, accumulate: true)
+    @phoenix_helpers Keyword.get(unquote(opts), :helpers, true)
+
+    import Phoenix.Router
+    import Plug.Conn
+    import Phoenix.Controller
+
+    # Set up initial scope
+    @phoenix_pipeline nil
+    Phoenix.Router.Scope.init(__MODULE__)
+    @before_compile unquote(__MODULE__)
+  end
+end
 ```
 
 **Why the deviation:** The Router needs to collect ALL routes, then compile them into a single dispatch function. This requires building up state during module compilation, then consuming it all at `@before_compile`.
@@ -68,7 +81,7 @@ Phoenix.Router.Scope.init(__MODULE__)
 
 **Phoenix Channel default:** `:temporary` (never restart).
 
-**Source:** `lib/phoenix/channel.ex:470-475`
+**Source:** `lib/phoenix/channel.ex:464-472`
 
 ```elixir
 def child_spec(init_arg) do
@@ -91,7 +104,7 @@ end
 
 **Phoenix Channel:** Defaults to hibernate after 15 seconds of inactivity.
 
-**Source:** `lib/phoenix/channel.ex:460`
+**Source:** `lib/phoenix/channel.ex:459`
 
 ```elixir
 @phoenix_hibernate_after Keyword.get(opts, :hibernate_after, 15_000)
@@ -115,7 +128,7 @@ end
 
 **Phoenix Endpoint:** Uses `Plug.Builder` — a macro that generates the `call/2` pipeline by chaining plugs at compile time.
 
-**Source:** `lib/phoenix/endpoint.ex:481-483`
+**Source:** `lib/phoenix/endpoint.ex:478-480`
 
 ```elixir
 defp plug() do
@@ -136,14 +149,20 @@ end
 
 **Phoenix exceptions:** Include `plug_status` for HTTP response mapping.
 
-**Source:** `lib/phoenix/router.ex:7-8`
+**Source:** `lib/phoenix/router.ex:2-26`
 
 ```elixir
 defmodule NoRouteError do
+  @moduledoc """
+  Exception raised when no route is found.
+  """
   defexception plug_status: 404, message: "no route found", conn: nil, router: nil
 end
 
 defmodule MalformedURIError do
+  @moduledoc """
+  Exception raised when the URI is malformed on matching.
+  """
   defexception [:message, plug_status: 400]
 end
 ```