capsules/fonts: JetBrainsMono-Regular.ttf as a raw-blob capsule (item 4.3.7b)

mkcapsule.c already ingests arbitrary non-.4th files as raw byte blobs
(validate_forth_blocks only applies to .4th filenames), so no hex/base64
text-encoding or tool changes are needed -- corrects the design premise
in FABRIC.md's 4.3.7b item text (see the FABRIC.md correction note this
commit carries). ttf_load_from_capsule() resolves the font capsule by
name, validates its content hash, and points ttf_font_t at the capsule
arena bytes directly, zero-copy.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

capsules/fonts/README.md

@@ -0,0 +1,30 @@
+# capsules/fonts/
+
+Font capsule for FABRIC.md items 4.3.7/4.3.7b (TrueType rendering, adjunct
+to the stroke font — §27.7).
+
+| File | License | Provenance |
+|------|---------|------------|
+| `JetBrainsMono-Regular.ttf` | SIL Open Font License, Version 1.1 | The JetBrains Mono Project Authors, copyright 2020 (https://github.com/JetBrains/JetBrainsMono). License string confirmed by reading the font's own embedded `name` table directly (`strings -e b JetBrainsMono-Regular.ttf`) — not taken on trust from the filename. |
+
+Chosen as the v1 test/default TTF font 2026-08-10 (FABRIC.md §27.7 "Update
+2026-08-10"), resolving that item's licensing-check blocker.
+
+**Embedded as a raw-binary capsule, not text-encoded.** `tools/mkcapsule.c`'s
+`process_file()` reads any regular file under `capsules/` as raw bytes and
+only runs the 64-char/16-line `.4th` text-block validation
+(`validate_forth_blocks()`) when the filename ends in `.4th` — everything
+else, including this `.ttf`, is stored byte-for-byte in the generated
+`capsule_arena[]` and content-hashed (xxHash64) exactly like every other
+capsule. Capsule name: `fonts:JetBrainsMono-Regular.ttf` (colon-separated
+relative path, per `build_capsule_name()`). Fetch it with
+`capsule_find_by_name()` (`include/starkernel/capsule.h`) — that returns
+`offset`/`length` into the arena without ever routing through
+`capsule_exec_payload()`, so nothing tries to interpret the font bytes as
+FORTH source. This superseded FABRIC.md §27.7 decision #3 (hex/base64
+text-encoding) — see that section's 2026-08-10 correction note.
+
+No SIL OFL 1.1 full license text is bundled here yet — only the font's own
+embedded attribution string. Add the full `OFL.txt` alongside this file if/
+when redistribution requirements are checked in detail (OFL requires the
+license text to accompany the font).