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/firmware_page.h

@@ -7,6 +7,7 @@
 
 #include "dialog_model.h"
 #include "key_event.h"
+#include "key_help.h"
 #include "list_model.h"
 #include "release_info.h"
 #include "services/storage_service.h"
@@ -28,6 +29,8 @@ class FirmwarePage {
     void enter();
     bool onKey(const KeyEvent& e);  // false: leave the page
     void draw(Canvas& c);
+    void help(std::vector<KeyHelp>& out) const;
+    const char* helpTitle() const;
 
    private:
     enum Row { kVersion, kStatus, kAddress, kLatest, kOlder, kSdHeader, kFixed };