chore: scaffold tvctl foundation

Set up the Rust crate, baseline module layout, and project docs so the
repository matches the design bundle and builds cleanly as a starting point.

src/daemon/cache.rs

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+use crate::adapters::AppInfo;
+
+/// A platform-level cache of app metadata discovered from live devices.
+#[derive(Debug, Clone, Default)]
+pub struct AppCache {
+    /// The normalized platform identifier for the cache file.
+    pub platform: String,
+    /// The apps currently known for that platform.
+    pub apps: Vec<AppInfo>,
+}

src/daemon/discovery.rs

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+/// Background discovery orchestration for supported TV platforms.
+#[derive(Debug, Clone, Default)]
+pub struct DiscoveryService;

src/daemon/mod.rs

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+pub mod cache;
+pub mod discovery;
+pub mod registry;
+pub mod state;
+
+/// The long-lived tvctld process.
+#[derive(Debug, Default)]
+pub struct Daemon;

src/daemon/registry.rs

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+use crate::adapters::Device;
+
+/// The persisted collection of known devices.
+#[derive(Debug, Clone, Default)]
+pub struct DeviceRegistry {
+    /// All devices currently remembered by the daemon.
+    pub devices: Vec<Device>,
+}

src/daemon/state.rs

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+use std::collections::HashMap;
+
+use uuid::Uuid;
+
+use crate::adapters::DeviceState;
+
+/// An in-memory cache of the last observed state for each device.
+#[derive(Debug, Clone, Default)]
+pub struct StateCache {
+    /// State entries keyed by device UUID.
+    pub entries: HashMap<Uuid, DeviceState>,
+}