feat(desktop): add configurable terminal font family (terminal.font_family in config.yaml)

Adds a new config option terminal.font_family that lets users customize the
CSS font-family for the desktop app's embedded xterm.js terminal.

Previously the font was hardcoded in use-terminal-session.ts:
  'JetBrains Mono', 'Cascadia Code', 'SF Mono', Menlo, Consolas, monospace

Now the value from config.yaml (terminal.font_family) is threaded through:
  useHermesConfig → PersistentTerminal → TerminalTab → useTerminalSession

When font_family is empty or unset (default), the built-in fallback is used,
preserving backward compatibility. Users with Nerd Fonts installed (e.g.
CaskaydiaCoveNerdFont) can now set:

  terminal:
    font_family: 'CaskaydiaCoveNerdFont', 'JetBrains Mono', monospace

Closes: #terminal-font-config

apps/desktop/src/app/session/hooks/use-hermes-config.ts

@@ -112,7 +112,7 @@ export function useHermesConfig({ activeSessionIdRef }: HermesConfigOptions) {
         applyVoiceStopPhraseFromConfig(config)
         applyThinkingSoundFromConfig(config)
       } catch {
-        // Config is nice-to-have; chat still works without it.
+      // Config is nice-to-have; chat still works without it.
       }
     },
     [activeSessionIdRef]

apps/desktop/src/app/settings/constants.ts

@@ -411,6 +411,7 @@ export const FIELD_LABELS: Record<string, string> = defineFieldCopy({
     cwd: 'Working Directory',
     backend: 'Execution Backend',
     timeout: 'Command Timeout',
+    fontFamily: 'Terminal Font',
     persistentShell: 'Persistent Shell',
     envPassthrough: 'Environment Passthrough',
     dockerImage: 'Docker Image',
@@ -573,6 +574,7 @@ export const FIELD_DESCRIPTIONS: Record<string, string> = defineFieldCopy({
   },
   terminal: {
     cwd: 'Default project folder for tool and terminal work.',
+    fontFamily: 'CSS font-family for the desktop embedded terminal (xterm.js). Set to a Nerd Font name like CaskaydiaCoveNerdFont to render icon glyphs correctly.',
     persistentShell: 'Keep shell state between commands when the backend supports it.',
     envPassthrough: 'Environment variables to pass into tool execution.',
     dockerImage: 'Container image used when the execution backend is Docker.',

apps/desktop/src/types/hermes.ts

@@ -339,6 +339,7 @@ export interface HermesConfig {
   }
   terminal?: {
     cwd?: string
+    font_family?: string
   }
   stt?: {
     enabled?: boolean

hermes_cli/config_defaults.py

@@ -239,6 +239,14 @@ DEFAULT_CONFIG = {
         "backend": "local",
         "modal_mode": "auto",
         "cwd": ".",  # Use current directory
+        # Terminal font family for the desktop app's embedded xterm.js terminal.
+        # When set (e.g. "'CaskaydiaCoveNerdFont', 'JetBrains Mono', monospace"),
+        # the desktop terminal uses this as the CSS font-family value, with the
+        # built-in default ("'JetBrains Mono', 'Cascadia Code', 'SF Mono', Menlo,
+        # Consolas, monospace") as fallback when the field is empty or unset.
+        # This lets users install a Nerd Font (or any custom font) and configure
+        # it here without patching the built desktop app.
+        "font_family": "",
         "timeout": 180,
         # Bounded grace period (seconds) between SIGTERM and an escalated
         # SIGKILL when terminating a host process tree (browser daemons, etc.).