iris: drop bundled Noto Sans, match Compose's platform-font fonts

Iris's call: "remove the font for now; just match what compose does."
Removes the six embedded Noto Sans/Noto Sans Mono TTFs (3.6 MB) that
TextData::default used to register ahead of the platform's own fonts;
fontique's system font discovery was already on by default and now
runs unshadowed (Roboto/Roboto Flex on Android, fontconfig on the
desktop). .so -3,748,136 bytes (11,193,608 -> 7,445,472), matching the
estimate. Verified fallback still lands on visible tofu for CJK/emoji
rather than blank, and flagged (not fixed) a fontique Android backend
gap that leaves Monospace unresolved -- see RUST.md's "Platform fonts
(2026-09-07)" and DECISIONS.md/IRIS.md's dated entries.

docs/IRIS.md

@@ -8,6 +8,27 @@ capability that moved. Small and trivial changes do not go here.
 An entry gives the date, what changed, why, and a short before/after where
 it helps judge the change without the session that made it. Newest first.
 
+## 2026-09-07: `TextData` no longer bundles a font
+
+Iris's call: "remove the font for now; just match what compose does."
+`TextData::default()` used to embed six Noto Sans/Noto Sans Mono `.ttf`s
+(3.6 MB, `include_bytes!`) and register them ahead of the platform's own
+fonts in the `SansSerif`/`Monospace` fallback lists. That registration is
+gone; `TextData::default()`'s signature is unchanged, but what it produces
+now depends entirely on `fontique`'s platform discovery (already on by
+default, previously shadowed) -- Roboto/Roboto Flex on Android, whatever
+the desktop's fontconfig resolves on Linux. No caller-visible type or
+method changed, but every consumer of `iris-core` text now renders with
+whatever the host platform's fonts are, not a fixed bundled face -- worth
+knowing if you were relying on pixel-identical text across devices.
+`.so` shrank by 3.75 MB. One real gap surfaced by the switch: this
+fontique version's Android backend never resolves the `Monospace`
+generic family (a fontique ordering bug, not new in this change), so
+`Family::Monospace` text falls through to the same face as
+`SansSerif` on Android rather than a true monospaced one -- still
+visible, not blank, just not monospaced. docs/RUST.md's "Platform fonts
+(2026-09-07)" has the full account.
+
 ## 2026-09-07: a headless harness, replayed touch, and physical-pixel desktop layout
 
 Layer 1 and 2 of docs/RUST.md's "Three test layers".