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The Site job fails when the data file is out of date or a page asks for a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

README.md

@@ -10,7 +10,7 @@ A multi-app firmware for the **M5Stack Cardputer ADV** with the **Cap LoRa-1262*
 
 ## On the device: one key
 
-**Fn+h, on any screen, lists the keys that work there** (`?` does the same outside a text field). No screen names its keys itself (docs/milestones/U1.md): each App declares them for the state it is in, and the help panel shows them, followed by the ones that work everywhere.
+**Fn+h, on any screen, lists the keys that work there** (`?` does the same outside a text field). No screen names its keys itself (docs/milestones/U1.md). Every screen's keys are one table in `lib/core/src/app_keys.h`: the help panel shows the table of the state an App is in, and the website's key tables are generated from the same file.
 
 ## Requirements