Have the beat prompt read all proposal attributes

Broaden the plot-beat system prompt beyond characters + plot: instruct
the model to read and honour every attribute the proposal states —
title, setting, genre, tone, characters, target age (adult / YA / middle
grade / …), and the loose plot summary. The beats now follow the stated
genre's conventions, keep the tone, and stay appropriate to the target
age; missing attributes are inferred rather than contradicted. Updates
the user-message framing and the README to match.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XDfaEsTgcn61n3wgP62DFF

README.md

@@ -177,8 +177,12 @@ using the [Mistral](https://mistral.ai/) chat API.
    `mistral-large-latest`) and the **Base URL** (default `https://api.mistral.ai`,
    handy if you route through a proxy). The settings are remembered.
 2. Choose **Tools ▸ Generate plot beats…** and pick a markdown (or text) file
-   describing the novel — its **characters** and a **loose plot summary**. The
-   request runs in the background, so the editor stays responsive.
+   describing the novel. Anything the file states is read and honoured — the
+   **title**, **setting**, **genre**, **tone**, **characters**, **target age**
+   (adult, young adult, …), and a **loose plot summary**; the beats follow the
+   genre's conventions, keep the tone, and stay age-appropriate. Missing
+   attributes are inferred from the rest. The request runs in the background, so
+   the editor stays responsive.
 3. The result opens in a **floating window** with the beats grouped under
    *Act I — Setup*, *Act II — Confrontation*, and *Act III — Resolution*, each a
    numbered list. You can **edit** the text in place, then: