Colour list markers by depth, highlight fences, draw images as links, and stream a list an item at a time

Items 1-5 of TRANSCRIPT_RENDERING.md's list, plus the AGP 9.4.0 bump from 7.
MarkdownRoot provides the renderer's locals itself instead of calling its
Markdown() composable; fences and indented blocks go through CodeFence.kt,
which shares the tool-input highlighter and a fence-language alias table;
an image in a paragraph is a link carrying its alt text, so every paragraph
is now platform text; LiveParse freezes the finished items of the tail list
so a forty-item list streams as forty paragraphs would.

Measured before, on the emulator (report from transcript-bench.sh over the
200-line fence fixture): draw phase 0.72ms per frame, transcript 0.36ms.
stream-bench.sh (new) streaming forty linked bullets on the old build:
markdown reparsed while streaming 483, 3.9ms mean, 11.6ms worst; record:
one block worst 1.6ms. The after runs, the on-screen check of the glyphs
and lint are recorded as owed in the doc's "What is next".

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

app/androidApp/src/main/kotlin/com/example/aiapp/Theme.kt

@@ -224,6 +224,19 @@ fun catppuccinSyntax(): SyntaxTheme =
 val linkColor: Color
     @Composable get() = Mocha.Blue
 
+/**
+ * A list's markers: the bullets and numbers down its left edge.
+ *
+ * The scheme's secondary accent rather than the text colour, because a marker is structure rather
+ * than words: coloured, the items of a list can be counted without reading them, and a nested list
+ * reads as a shape before it reads as text. Lavender is not one of the colours that mean something
+ * here -- green, red, peach and yellow are states and actions -- and it is the same at every depth,
+ * since depth is said by the glyph and the indent; a colour per depth would make a difference in
+ * degree look like one in kind.
+ */
+val listMarkerColor: Color
+    @Composable get() = Mocha.Lavender
+
 /** Past a limit. The scheme's error colour, for the reason [failedColor] gives. */
 val overLimitColor: Color
     @Composable get() = MaterialTheme.colorScheme.error