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The Site job fails when the data file is out of date or a page asks for a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

site/templates/shortcodes/keys.html

@@ -0,0 +1,18 @@
+{#- The keys of one or more screens, as the help panel (Fn+h) lists them on the device:
+    {{ keys(scopes=["storage", "storage-details"]) }}, or {{ keys(all=true) }} for every screen.
+    The tables come from site/data/keys.toml, generated from lib/core/src/app_keys.h (issue #72):
+    a key added to an App shows up here without anyone editing a page. -#}
+{%- set data = load_data(path="data/keys.toml", format="toml") -%}
+{%- set everything = all is defined and all -%}
+<div class="keys">
+{%- for s in data.scope %}{% if everything or (scopes is defined and s.id in scopes) %}
+<div class="keys-scope">
+<h4 id="keys-{{ s.id }}">{{ s.title }}</h4>
+<table>
+{%- for r in s.rows %}
+<tr><td><kbd>{{ r.0 }}</kbd></td><td>{{ r.1 }}</td></tr>
+{%- endfor %}
+</table>
+</div>
+{%- endif %}{% endfor %}
+</div>