Help: Fn+h lists the keys of the screen you're on, and no screen names its keys any more (#69)

Fn+h on any screen, text fields included, and ? outside Text Entry, open a
panel over the content area: the screen's own keys, then the ones that work
everywhere. Every App declares its keys for the state it is in (pages,
viewers, dialogs and text fields answer for themselves); the App manager
opens the panel and takes every key while it is open.

About 30 hint lines are gone, from every App. What stays on a screen is
state. The first-start Setup keeps its hints and teaches the key; a device
set up before gets one Toast, once. The guide and the FAQ open with it.
`key help` over the consoles.

476 host tests (8 new). Checked on the device with key help and screenshots:
the Launcher, all nine Apps and several of their states. 8.5 KB of flash and
40 bytes of static RAM. Decisions Q196 to Q203 in docs/milestones/U1.md.

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

src/apps/note_editor.cpp

@@ -182,6 +182,18 @@ bool NoteEditor::save() {
     return true;
 }
 
+void NoteEditor::help(std::vector<KeyHelp>& out) const {
+    if (dialog_) return help::dialog(out);
+    out.push_back({"Enter", "a new line"});
+    out.push_back({"Del", "delete backwards"});
+    out.push_back({"Tab", "two spaces"});
+    out.push_back({"Fn ; . , /", "move the cursor"});
+    out.push_back({"Alt Fn ; .", "a page up, down"});
+    out.push_back({"Ctrl a  e", "start, end of the line"});
+    out.push_back({"opt ' e", "an accent: \xC3\xA9"});
+    out.push_back({"`", "done: it saves by itself"});
+}
+
 bool NoteEditor::onKey(const KeyEvent& e) {
     if (!text_) return false;
     redraw_ = true;
@@ -290,7 +302,7 @@ void NoteEditor::draw(Canvas& c) {
     c.setFont(&fonts::small);
     bool showMessage = !message_.empty() && millis() - messageMs_ < kMessageMs;
     c.setTextColor(showMessage ? theme::kWarning : theme::kMuted);
-    c.drawString(showMessage ? message_.c_str() : "Fn+arrows: move  Ctrl+A/E: line  Back: done", 4, area.y + area.h - 9);
+    if (showMessage) c.drawString(message_.c_str(), 4, area.y + area.h - 9);
 
     if (dialog_ && ask_ == Ask::Recover)
         widgets::dialog(c, "Unsaved copy", "A save of this note was cut short. Its copy has " + formatBytes(recovered_.size()) + ", the note " +