feat(host): PUNKTFUNK_HOST_NAME names the host in Moonlight and the clients

A box called `bazzite-htpc` had no way to present itself as "Living Room"
short of renaming the machine. The new knob overrides the name everywhere
a human sees it: the GameStream serverinfo <hostname> element and the
mDNS service instance name both adverts carry. Unset (the default) is the
machine's own hostname, exactly as before.

Free text is the point, so the DNS-level name is now a separate concern
from the display name. The instance label may contain spaces and accents;
an A-record target may not, and mdns-sd rejects the whole ServiceInfo if
the target is not a legal name — which would take discovery down rather
than merely look wrong. dns_label() sanitizes the target and passes an
already-legal name through byte-for-byte, so hosts without the override
advertise precisely what they always did. The display name loses `.` (it
would split the label, and clients derive the name as the first label of
the fullname, so "Ben's PC v1.2" would arrive as "Ben's PC v1") and is
capped at the 63-byte DNS-SD ceiling on a char boundary.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
(cherry picked from commit bbf72261a12e0e67601f549d40db65ae61979268)

crates/pf-host-config/src/lib.rs

@@ -61,6 +61,12 @@ pub fn env_on(name: &str) -> Option<bool> {
 /// derived `Debug` impl, so the parser can stay a single platform-neutral function.
 #[derive(Debug, Clone, Default)]
 pub struct HostConfig {
+    /// `PUNKTFUNK_HOST_NAME` — the name this host shows up under in Moonlight (the serverinfo
+    /// `<hostname>` element) and in Punktfunk's own clients (the mDNS service *instance* name both
+    /// adverts carry). Unset/blank = the machine's own hostname, which is what it always was. Free
+    /// text ("Living Room PC"); the DNS-level `<label>.local.` target keeps using a sanitized
+    /// machine-safe label, so a spacey display name can't produce an invalid mDNS record.
+    pub host_name: Option<String>,
     /// `PUNKTFUNK_ENCODER` — explicit encoder-backend override (lowercased; empty = auto-detect by GPU vendor).
     pub encoder_pref: String,
     /// `PUNKTFUNK_RENDER_ADAPTER` — discrete render-GPU pin by description substring (`Some` even when empty:
@@ -159,6 +165,9 @@ impl HostConfig {
             // (`PUNKTFUNK_IDD_PUSH` was removed: IDD-push is the sole Windows capture path, so the knob
             // only split dispatch — capture ignored it while the vdisplay manager obeyed it, and `=0`
             // produced dead-swap-chain reuse on reconnect. A stale setting in an old host.env is ignored.)
+            host_name: val("PUNKTFUNK_HOST_NAME")
+                .map(|s| s.trim().to_string())
+                .filter(|s| !s.is_empty()),
             encoder_pref: std::env::var("PUNKTFUNK_ENCODER")
                 .unwrap_or_default()
                 .to_ascii_lowercase(),