feat: rewrite the options page for first-time users (#23)

Rewrites the options page for first-time users without removing any setting. Customization in a lightweight package is what sets this extension apart. Design: `docs/superpowers/specs/2026-10-18-options-page-for-first-time-users-design.md`.

**User-visible changes**
- **Layout:** the description stays as the first line, followed by a **Usage instructions** section and the **Settings** section. Each section has a heading and a divider.
- **Usage instructions:** one labelled line per way to open ChatGPT, each with a small drawing:
  - **Address bar:** `<Ctrl>+L`, then `gpt`, a space and the question. The drawing shows a ChatGPT label because the address-bar code shipped in Firefox 157.0.1 enters search mode when an engine keyword is followed by a space. I checked that in its `omni.ja`, but it still needs confirming on screen; see the checks below.
  - **Right-click:** a drawing of the menu with Ask ChatGPT highlighted.
  - **Keyboard:** key caps for the user's actual shortcut, held down. The line is hidden when no shortcut is set.
  - **Toolbar:** the hovered button with the pointer, its tooltip, the puzzle-piece Extensions button, and a selected heading.
- **Drawings:** they are HTML/CSS and inline SVG, not screenshots, so they follow light and dark themes, stay sharp, and never go stale. They are centred. The package grows from 52.8 KB to 56.5 KB.
- **Settings:**
  - **Right-click menu** (was "Context menu") and **Open ChatGPT in** stay visible.
  - Choosing **Advanced** reveals a drawing of the Ask ChatGPT submenu (Ask normally, Explain, Summarize, Debug code). It lives in the block that only shows for Advanced, so it needs no script.
  - Prompt template, temporary chat and web search move under **More options**, whose heading names them. It opens by itself on load, or when a sync changes one of them, if one of them isn't at its default.
  - **Restore defaults** is right-aligned and red.
- **Bottom of the page:**
  - The keyword/default-engine and keyboard-shortcut notes become collapsed sections with numbered steps.
  - The project links are centred, and stack on narrow panels.
- **Hotkeys:** written as `<Ctrl>+L` and `<Alt>+<Shift>+G`, including the user's actual shortcut. Mac users see `<Cmd>`, `<Option>` and `<Return>`, detected with `runtime.getPlatformInfo`, which needs no permission.
- **Docs:**
  - Keyword wording is corrected in the options page and README: Firefox adds a custom keyword alongside `gpt` instead of replacing it.
  - README and AGENTS.md use the new setting names.
  - AGENTS.md records the keep-every-setting rule, the hotkey format and the "filled in, never sent" copy rule.

These still match the original options design spec: the temporary-chat and web-search wording, and the rule that copy never says the question is sent.

No permission, search URL, privacy or packaging changes.

**Checks**
- `npm test`: lint 0 errors / 0 warnings, 61/61 unit tests, build OK.
- New tests:
  - the key formatter, including the Mac names Firefox stores (Command, MacCtrl, Alt)
  - the page's written hotkeys match the formatter
  - the keyboard drawing's key caps follow the live shortcut
- Rendered in headless Firefox 157 with the extension APIs stubbed:
  - light and dark themes
  - 680 px and 360 px wide
  - Mac key names
  - More options opening for a customised prompt template
  - both bottom sections expanded

**Manual Firefox checks (`npm run dev` → about:addons → Preferences)**
- [x] Typing `gpt` and a space shows a ChatGPT label in the address bar, as drawn. If it doesn't, the drawing drops the label and shows plain `gpt how do magnets work?`
- [x] Light and dark themes, and a narrow about:addons width
- [x] Expanding More options and the two bottom sections grows the inline panel without clipping or scrolling
- [x] The Keyboard line and its key caps disappear when the shortcut is removed, and come back showing the new keys when one is set
- [x] More options opens by itself after changing the prompt template and reopening the page
- [x] Choosing Advanced shows the submenu drawing; Simple and Off hide it
- [x] Settings still save, and Restore defaults still works

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://git.zavage.net/Zavage-Software/search-with-chatgpt-powered-by-openai-extension/pulls/23
Co-authored-by: golem <golem@zavage.net>

AGENTS.md

@@ -35,6 +35,17 @@ Firefox Desktop is the only current implementation and release target. Do not ad
 
 Use two-space indentation in JSON, YAML, and JavaScript configuration. Preserve logical key grouping in `manifest.json`. Use lowercase, hyphenated filenames and include dimensions in icon names. Keep changes focused and avoid adding runtime dependencies without a concrete need.
 
+## Options Page
+
+- Keep every setting. Customization in a lightweight extension is what sets
+  this one apart, so simplify wording and layout, but never remove a setting
+  without the maintainer's agreement. Less-used settings can sit under
+  **More options**.
+- Write hotkeys as `<Ctrl>+L`: named keys in angle brackets, single characters
+  plain. `options/shortcut.js` swaps in Mac key names.
+- Say that ChatGPT opens with the text filled in, never that the text is sent,
+  searched, or asked. The options design spec explains why.
+
 ## Testing Guidelines
 
 Unit tests cover the pure logic in `lib/` via `node:test`; automated checks
@@ -46,10 +57,12 @@ After `npm test`, use `npm run dev` and confirm:
 
 - `gpt <query>` opens ChatGPT, the provider stays non-default, and Firefox
   search settings can configure it.
-- The Options/Preferences tab renders the settings plus Restore defaults,
+- The Options/Preferences tab renders the drawings, every setting (including
+  those under More options), and Restore defaults,
   in both light and dark themes and at a narrow window width, and values
-  persist across a restart.
-- **Context menu → Simple** shows the direct **Ask ChatGPT** item only for
+  persist across a restart. Expanding and collapsing More options and the
+  collapsed sections resizes the inline panel without clipping or scrolling.
+- **Right-click menu → Simple** shows the direct **Ask ChatGPT** item only for
   selected text. **Advanced** shows the contextual submenu; selection takes
   precedence over links. **Off** hides the menu. Switch modes without restarting
   and confirm Alt+Shift+G still works in every mode. Restore defaults returns
@@ -74,7 +87,7 @@ After `npm test`, use `npm run dev` and confirm:
     stale cross-origin frame silently seeding the prompt was the worse failure.
 - Click the **Ask ChatGPT** toolbar button with no selection, a top-frame
   selection, and an iframe selection after a stale top-frame selection.
-  Check restricted-page fallback, context menu Off, saved prompt and opening
+  Check restricted-page fallback, right-click menu Off, saved prompt and opening
   preferences, and consent before shortening long selections. Test both the
   pinned toolbar button and its entry in Firefox’s extensions menu.