feat(quartz): theme parser tags for kind-30312 (T3 #1)

Adds the Tier-3 minimum-viable theming primitives so a themed
nostrnests room renders without crashing the client:

  ColorTag       — `["c", "<hex6>", "background"|"text"|"primary"]`.
                   Strict 6-char hex parser; `#abc` shorthand and
                   named colors are REJECTED so a typo'd room
                   event can't crash the renderer. Output hex is
                   normalised uppercase, no `#` prefix.
  BackgroundTag  — `["bg", "<url>", "tile"|"cover"]`. Mode defaults
                   to COVER when missing; unknown modes (a future
                   "blur") fall back to COVER until the renderer
                   learns them. Empty URL is rejected.

  MeetingSpaceEvent.colors() / .background() — tag accessors. The
  font tag (`["f", family, optionalUrl]`) is intentionally NOT in
  this commit; loading a custom FontFamily would need a per-pack
  loader, and font-less rooms still render fine on the client.

Tests:
  ColorTagTest — happy path, no-`#` prefix, rejects shorthand /
                 named / unknown target / missing target;
                 assemble normalisation; round-trip.
  BackgroundTagTest — happy path, default-COVER, future-mode
                       fallback, rejects empty URL, round-trip.

The Compose `RoomTheme` projection + `AudioRoomThemedScope`
renderer come next.

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

@@ -0,0 +1,64 @@
+/*
+ * 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.assertNull
+
+class BackgroundTagTest {
+    @Test
+    fun parseValidWithMode() {
+        val parsed = BackgroundTag.parse(arrayOf("bg", "https://i/x.jpg", "tile"))
+        assertEquals("https://i/x.jpg", parsed?.url)
+        assertEquals(BackgroundTag.Mode.TILE, parsed?.mode)
+    }
+
+    @Test
+    fun defaultsToCoverWhenModeMissing() {
+        val parsed = BackgroundTag.parse(arrayOf("bg", "https://i/x.jpg"))
+        assertEquals(BackgroundTag.Mode.COVER, parsed?.mode)
+    }
+
+    @Test
+    fun unknownModeFallsBackToCover() {
+        // Spec evolution — a future "blur" mode must not crash the
+        // parser. Falls back to COVER until the renderer learns the
+        // new mode.
+        val parsed = BackgroundTag.parse(arrayOf("bg", "https://i/x.jpg", "blur"))
+        assertEquals(BackgroundTag.Mode.COVER, parsed?.mode)
+    }
+
+    @Test
+    fun rejectsEmptyUrl() {
+        assertNull(BackgroundTag.parse(arrayOf("bg", "")))
+    }
+
+    @Test
+    fun assembleRoundTrips() {
+        val tag = BackgroundTag.assemble("https://i/p.png", BackgroundTag.Mode.TILE)
+        val parsed = BackgroundTag.parse(tag)
+        assertEquals(
+            BackgroundTag(url = "https://i/p.png", mode = BackgroundTag.Mode.TILE),
+            parsed,
+        )
+    }
+}

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

@@ -0,0 +1,76 @@
+/*
+ * 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.assertNull
+
+class ColorTagTest {
+    @Test
+    fun parsesValidHexAndTarget() {
+        val parsed = ColorTag.parse(arrayOf("c", "#FF8800", "background"))
+        assertEquals("FF8800", parsed?.hex)
+        assertEquals(ColorTag.Target.BACKGROUND, parsed?.target)
+    }
+
+    @Test
+    fun parsesWithoutHashPrefix() {
+        val parsed = ColorTag.parse(arrayOf("c", "abcdef", "primary"))
+        assertEquals("ABCDEF", parsed?.hex)
+        assertEquals(ColorTag.Target.PRIMARY, parsed?.target)
+    }
+
+    @Test
+    fun rejectsShortHex() {
+        // `#abc` shorthand is rejected — keeps the parser strict so
+        // a typo'd room event can't crash the renderer.
+        assertNull(ColorTag.parse(arrayOf("c", "#abc", "text")))
+    }
+
+    @Test
+    fun rejectsNamedColors() {
+        assertNull(ColorTag.parse(arrayOf("c", "red", "text")))
+    }
+
+    @Test
+    fun rejectsUnknownTarget() {
+        assertNull(ColorTag.parse(arrayOf("c", "#abcdef", "accent")))
+    }
+
+    @Test
+    fun rejectsMissingTarget() {
+        assertNull(ColorTag.parse(arrayOf("c", "#abcdef")))
+    }
+
+    @Test
+    fun assembleProducesUppercaseNoHash() {
+        val tag = ColorTag.assemble("#abcdef", ColorTag.Target.TEXT)
+        assertEquals(arrayOf("c", "ABCDEF", "text").toList(), tag.toList())
+    }
+
+    @Test
+    fun roundTripPreservesEverything() {
+        val tag = ColorTag.assemble("FF00FF", ColorTag.Target.PRIMARY)
+        val parsed = ColorTag.parse(tag)
+        assertEquals(ColorTag(hex = "FF00FF", target = ColorTag.Target.PRIMARY), parsed)
+    }
+}