Add the dashboard settings channel, wired for theme and lock

A dashboard could only ever receive as a set of tiles. This adds the dashboard
itself as a receiver: `settings` maps a name to a value plus an optional
binding. Unbound, the setting is simply its value — a wall panel that is always
dark costs no flow. Bound, a flow drives it live and the value is the fallback.

Two settings are wired: `theme` (system/light/dark) and `locked` (read-only).
There is no schedule field on purpose — a node publishing to the bound message
on a cron is what a schedule is here, which is the point of a channel.

- `messages_for()` now walks a dashboard's bound settings as well as its
  widgets' bindings. Without this a paired screen is refused its own theme
  message, on the one surface the setting exists for; it bounds the socket too.
- `locked` is gated in `usePublish`, so every control inherits it, and each
  control also draws itself disabled — a dead button reads as broken otherwise.
  The panel surface says Read-only in the corner.
- The theme is a class on the dashboard's own surface, never the root: inside
  the app shell it must not flip the chrome. `.light` gains the tokens `.dark`
  already had (mirrored in the index repo) so both directions work on a subtree.
- Settings bindings are type-checked from the document alone, the rule widget
  bindings follow, and mirrored on the server.
- A bound setting is drawn on the flow canvas as a dashboard-level endpoint.
- The demo's house flow now publishes `home.panel_theme`, which the demo
  dashboard's theme binds to: the panel goes dark after sunset, at no tile cost.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tULRZJUkZsw7rMJ3h4xvu

frontend/src/client/schemas.gen.ts

@@ -435,6 +435,13 @@ export const DashboardDef_InputSchema = {
             type: 'array',
             title: 'Pages'
         },
+        settings: {
+            additionalProperties: {
+                '$ref': '#/components/schemas/SettingDef'
+            },
+            type: 'object',
+            title: 'Settings'
+        },
         version: {
             type: 'integer',
             title: 'Version',
@@ -496,6 +503,13 @@ export const DashboardDef_OutputSchema = {
             type: 'array',
             title: 'Pages'
         },
+        settings: {
+            additionalProperties: {
+                '$ref': '#/components/schemas/SettingDef'
+            },
+            type: 'object',
+            title: 'Settings'
+        },
         version: {
             type: 'integer',
             title: 'Version',
@@ -2640,6 +2654,36 @@ export const SeriesPointSchema = {
     title: 'SeriesPoint'
 } as const;
 
+export const SettingDefSchema = {
+    properties: {
+        value: {
+            title: 'Value'
+        },
+        message: {
+            type: 'string',
+            title: 'Message',
+            default: ''
+        },
+        dtype: {
+            type: 'string',
+            title: 'Dtype',
+            default: ''
+        }
+    },
+    type: 'object',
+    title: 'SettingDef',
+    description: `One dashboard-wide setting: a value, and optionally where it comes from.
+
+Unbound — no \`\`message\`\` — the setting is simply \`\`value\`\`, which is what
+makes a panel that is always dark cost no flow at all. Bound, a flow drives
+it live and \`\`value\`\` is the fallback: what the dashboard uses until
+something arrives, and whenever the message is silent.
+
+A schedule is not a third case. A node publishing to the bound message on a
+cron *is* the schedule, which is the whole reason this is a channel rather
+than a switching rule per setting.`
+} as const;
+
 export const ShareRequestSchema = {
     properties: {
         lib_name: {

frontend/src/client/types.gen.ts

@@ -117,6 +117,9 @@ export type DashboardDef_Input = {
     canvas_height?: number;
     icon?: string;
     pages?: Array<PageDef_Input>;
+    settings?: {
+        [key: string]: SettingDef;
+    };
     version?: number;
     has_draft?: boolean;
 };
@@ -132,6 +135,9 @@ export type DashboardDef_Output = {
     canvas_height?: number;
     icon?: string;
     pages?: Array<PageDef_Output>;
+    settings?: {
+        [key: string]: SettingDef;
+    };
     version?: number;
     has_draft?: boolean;
 };
@@ -919,6 +925,24 @@ export type SeriesPoint = {
     avg_lag_ms: number;
 };
 
+/**
+ * One dashboard-wide setting: a value, and optionally where it comes from.
+ *
+ * Unbound — no ``message`` — the setting is simply ``value``, which is what
+ * makes a panel that is always dark cost no flow at all. Bound, a flow drives
+ * it live and ``value`` is the fallback: what the dashboard uses until
+ * something arrives, and whenever the message is silent.
+ *
+ * A schedule is not a third case. A node publishing to the bound message on a
+ * cron *is* the schedule, which is the whole reason this is a channel rather
+ * than a switching rule per setting.
+ */
+export type SettingDef = {
+    value?: unknown;
+    message?: string;
+    dtype?: string;
+};
+
 export type ShareRequest = {
     lib_name: string;
 };