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/DECISIONS.md

@@ -5,6 +5,40 @@ they can be judged and reversed later. Detail lives in RUST.md (and IRIS.md
 for iris API changes); this file is only the summary. Newest first. Items
 marked **DEFERRED** are ones the agent chose not to decide alone.
 
+## 2026-09-07 (platform fonts, not bundled ones)
+
+- **Iris's own decision, carried out as directed**: removed the 3.6 MB of
+  bundled Noto Sans/Noto Sans Mono TTFs from `iris-core` and load text
+  from the platform's own font collection instead (`fontique`'s system
+  discovery, already on by default). Matches what the Compose app does --
+  it takes body text from `FontFamily.Default` and code text from
+  `FontFamily.Monospace`, both platform-resolved, and ships no text font
+  of its own. Rejected alternative (the one this pass had left open
+  2026-09-06): subsetting the bundled Noto Sans to Latin/common
+  punctuation instead of removing it outright, which would have kept
+  identical rendering across devices for a smaller (not zero) size cost;
+  Iris chose to match Compose instead.
+- `.so` **-3,748,136 bytes** (11,193,608 -> 7,445,472), matching the
+  original 3.6 MB estimate. Fallback still lands on the platform's own
+  tofu for a codepoint no resolved face has (checked with CJK + emoji on
+  desktop) rather than blank space, so the UI_RULES unknown-glyph rule
+  still holds.
+- **Flagging for Iris, not blocking on it**: this fontique version's
+  Android backend never resolves the `Monospace` generic family at all
+  (confirmed on this checkout's emulator, `mono=None` in the startup
+  diagnostic) -- a pre-existing ordering bug in fontique's own
+  `fonts.xml` parsing, not something this change introduced, but this
+  change is what stopped masking it (the bundled mono font used to be
+  registered ahead of the broken platform lookup, so it always won).
+  Effect: code blocks and the tool-card chevron marks fall through to
+  the same face as body text on Android instead of a genuinely
+  monospaced one -- still visible, not blank, just not monospaced.
+  Compose does not share this gap; it resolves `FontFamily.Monospace`
+  through Android's own `Typeface.MONOSPACE`, not through fontique.
+  docs/RUST.md's "Platform fonts (2026-09-07)" has the full account and
+  why a fix (an OEM-specific named-family pin, or patching around
+  fontique) is left as a follow-up rather than done in this pass.
+
 ## 2026-09-06 (how a tool call looks, P1b)
 
 - **A card that never got a result says "no result", in yellow, and it is