feat(audio-rooms): font-tag parser + system-font typography (T3 #1)

Closes the deferred font tag from the Tier-3 plan. Wire-up:

  * quartz: FontTag(family, optionalUrl) parser/assembler with
    blank-rejection on family + blank-URL-becomes-null normalisation.
  * MeetingSpaceEvent.font(): FontTag? accessor.
  * TagArrayBuilder.font(family, url) DSL.
  * RoomTheme gains fontFamily / fontUrl fields.
  * AudioRoomThemedScope maps `family` to a Compose FontFamily for
    the four CSS-style generic-family names ("sans-serif", "serif",
    "monospace", "cursive") — each maps to the corresponding system
    fallback. The whole Material3 typography is rebuilt with that
    family so headlines / body / labels all swap together.

URL-based font loading (RoomTheme.fontUrl) is the natural follow-up:
fetch + cache via OkHttp, then build a FontFamily from a local
file. Until then, an unknown family is silently a no-op — the room
renders in the platform default rather than crashing or fetching
on the UI thread.

Tests:
  * FontTagTest — 9 cases covering family-only, family+URL,
    blank rejection, missing family, wrong tag name, blank-URL
    normalisation, assembler shapes (with + without URL), and
    the assembler's blank-family rejection.
  * RoomThemeTest gains 3 cases for font projection (family-only /
    family+URL / empty event).

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/meetingSpaces/tags/FontTagTest.kt

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertNotNull
+import kotlin.test.assertNull
+
+class FontTagTest {
+    @Test
+    fun parsesFamilyOnly() {
+        val parsed = FontTag.parse(arrayOf("f", "Inter"))
+        assertNotNull(parsed)
+        assertEquals("Inter", parsed.family)
+        assertNull(parsed.url)
+    }
+
+    @Test
+    fun parsesFamilyWithUrl() {
+        val parsed = FontTag.parse(arrayOf("f", "Inter", "https://fonts.example/inter.woff2"))
+        assertNotNull(parsed)
+        assertEquals("Inter", parsed.family)
+        assertEquals("https://fonts.example/inter.woff2", parsed.url)
+    }
+
+    @Test
+    fun rejectsBlankFamily() {
+        // A blank family is not actionable for the renderer — match
+        // ColorTag's strictness rather than letting an empty value
+        // through and surprising the typography fallback.
+        assertNull(FontTag.parse(arrayOf("f", "")))
+        assertNull(FontTag.parse(arrayOf("f", "  ")))
+    }
+
+    @Test
+    fun rejectsMissingFamily() {
+        assertNull(FontTag.parse(arrayOf("f")))
+    }
+
+    @Test
+    fun rejectsWrongName() {
+        assertNull(FontTag.parse(arrayOf("font", "Inter")))
+    }
+
+    @Test
+    fun blankUrlBecomesNull() {
+        // A blank third element is treated as "no URL" rather than
+        // an empty URL — otherwise the renderer would attempt an
+        // HTTP fetch for "" and fail at the URL parser.
+        val parsed = FontTag.parse(arrayOf("f", "Inter", ""))
+        assertNotNull(parsed)
+        assertNull(parsed.url)
+    }
+
+    @Test
+    fun assembleFamilyOnly() {
+        assertEquals(
+            arrayOf("f", "Inter").toList(),
+            FontTag.assemble("Inter").toList(),
+        )
+    }
+
+    @Test
+    fun assembleWithUrl() {
+        assertEquals(
+            arrayOf("f", "Inter", "https://fonts.example/inter.woff2").toList(),
+            FontTag.assemble("Inter", "https://fonts.example/inter.woff2").toList(),
+        )
+    }
+
+    @Test
+    fun assembleRejectsBlankFamily() {
+        assertFailsWith<IllegalArgumentException> { FontTag.assemble("") }
+    }
+}