Keys: one table file for the device's help panel and the website's key tables (#72)

Every screen's keys are constant tables in lib/core/src/app_keys.h (52 of
them, each under an `// id: Title` comment). An App's help() picks the table
of the state it is in. site/tools/gen_dev_docs.py reads the same file and
writes site/data/keys.toml; the `keys` shortcode shows a screen's tables on
its guide page, and /guide/keys/ shows all of them.

The Site job fails when the data file is out of date or a page asks for a
table that doesn't exist, and now also runs when app_keys.h changes. A key
added to an App shows up on the website without anyone editing a page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/apps/settings_app.cpp

@@ -1,3 +1,4 @@
+#include "app_keys.h"
 #include "settings_app.h"
 
 #include <Arduino.h>
@@ -131,12 +132,9 @@ bool SettingsApp::onAboutKey(const KeyEvent& e) {
 
 void SettingsApp::help(std::vector<KeyHelp>& out) const {
     switch (page_) {
-        case Page::Menu:
-            help::list(out, "edit, or open the page");
-            out.push_back({", /", "change a switch or a slider"});
-            break;
-        case Page::Text: help::textEntry(out); break;
-        case Page::Choice: help::list(out, "choose it"); break;
+        case Page::Menu: keys::add(out, keys::kSettings); break;
+        case Page::Text: keys::add(out, keys::kText); break;
+        case Page::Choice: keys::add(out, keys::kSettingsChoice); break;
         case Page::About: break;
         case Page::Wifi: wifiPage_.help(out); break;
         case Page::Firmware: firmwarePage_.help(out); break;