feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/defmt-macros/src/items/bitflags/input.rs

@@ -0,0 +1,93 @@
+use syn::{
+    parse::{Parse, ParseStream},
+    punctuated::Punctuated,
+    token, Attribute, Expr, Ident, Token, Type, Visibility,
+};
+
+#[allow(dead_code)]
+pub(super) struct Input {
+    struct_attrs: Vec<Attribute>,
+    vis: Visibility,
+    struct_token: Token![struct],
+    ident: Ident,
+    colon_token: Token![:],
+    ty: Type,
+    brace_token: token::Brace,
+    flags: Punctuated<Flag, Token![;]>,
+}
+
+impl Parse for Input {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let flags;
+        Ok(Self {
+            struct_attrs: Attribute::parse_outer(input)?,
+            vis: input.parse()?,
+            struct_token: input.parse()?,
+            ident: input.parse()?,
+            colon_token: input.parse()?,
+            ty: input.parse()?,
+            brace_token: syn::braced!(flags in input),
+            flags: Punctuated::parse_terminated(&flags)?,
+        })
+    }
+}
+
+impl Input {
+    pub(super) fn flags(&self) -> impl Iterator<Item = &Flag> {
+        self.flags.iter()
+    }
+
+    pub(super) fn ident(&self) -> &Ident {
+        &self.ident
+    }
+
+    pub(super) fn ty(&self) -> &Type {
+        &self.ty
+    }
+}
+
+#[allow(dead_code)]
+pub(super) struct Flag {
+    cfg_attrs: Vec<Attribute>,
+    const_attrs: Vec<Attribute>,
+    const_token: Token![const],
+    ident: Ident,
+    eq_token: Token![=],
+    value: Expr,
+}
+
+impl Parse for Flag {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let const_attrs = Attribute::parse_outer(input)?;
+        Ok(Self {
+            cfg_attrs: extract_cfgs(&const_attrs),
+            const_attrs,
+            const_token: input.parse()?,
+            ident: input.parse()?,
+            eq_token: input.parse()?,
+            value: input.parse()?,
+        })
+    }
+}
+
+impl Flag {
+    pub(super) fn cfg_attrs(&self) -> &[Attribute] {
+        &self.cfg_attrs
+    }
+
+    pub(super) fn ident(&self) -> &Ident {
+        &self.ident
+    }
+}
+
+fn extract_cfgs(attrs: &[Attribute]) -> Vec<Attribute> {
+    let mut cfgs = vec![];
+
+    for attr in attrs {
+        if attr.path().is_ident("cfg") {
+            cfgs.push(attr.clone());
+        }
+    }
+
+    cfgs
+}