chore: add agentic tooling, cleanup

.crosslink/rules/elixir-phoenix.md

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+# Phoenix & LiveView Rules
+
+## HEEx Template Syntax (Critical)
+- **Attributes use `{}`**: `<div id={@id}>` — never `<%= %>` in attributes
+- **Body values use `{}`**: `{@value}` — use `<%= %>` only for blocks (if/for/cond)
+- **Class lists require `[]`**: `class={["base", @flag && "active"]}` — bare `{}` is invalid
+- **No `else if`**: Use `cond` for multiple conditions
+- **Comments**: `<%!-- comment --%>`
+- **Literal curlies**: Use `phx-no-curly-interpolation` on parent tag
+
+## Phoenix v1.8
+- Wrap templates with `<Layouts.app flash={@flash}>` (already aliased)
+- `current_scope` errors → move routes to proper `live_session`, pass to Layouts.app
+- `<.flash_group>` only in layouts.ex
+- Use `<.icon name="hero-x-mark">` for icons, `<.input>` for form fields
+
+## LiveView
+- Use `<.link navigate={}>` / `push_navigate`, not deprecated `live_redirect`
+- Hooks with own DOM need `phx-update="ignore"`
+- Avoid LiveComponents unless necessary
+- No inline `<script>` tags — use assets/js/app.js
+
+## Streams (Always use for collections)
+```elixir
+stream(socket, :items, items)           # append
+stream(socket, :items, items, at: -1)   # prepend
+stream(socket, :items, items, reset: true)  # filter/refresh
+```
+Template: `<div id="items" phx-update="stream">` with `:for={{id, item} <- @streams.items}`
+- Streams aren't enumerable — refetch + reset to filter
+- Empty states: `<div class="hidden only:block">Empty</div>` as sibling
+
+## Forms
+```elixir
+# LiveView: always use to_form
+assign(socket, form: to_form(changeset))
+```
+```heex
+<%!-- Template: always @form, never @changeset --%>
+<.form for={@form} id="my-form" phx-submit="save">
+  <.input field={@form[:name]} type="text" />
+</.form>
+```
+- Never `<.form let={f}>` or `<.form for={@changeset}>`
+
+## Router
+- Scope alias is auto-prefixed: `scope "/", AppWeb do` → `live "/users", UserLive` = `AppWeb.UserLive`
+
+## Ecto
+- Preload associations accessed in templates
+- Use `Ecto.Changeset.get_field/2` to read changeset fields
+- Don't cast programmatic fields (user_id) — set explicitly
+
+## Testing
+- Use `has_element?(view, "#my-id")`, not raw HTML matching
+- Debug selectors: `LazyHTML.filter(LazyHTML.from_fragment(render(view)), "selector")`
+