font.4th: TEXT entry point, UTF-8 string rendering (item 4.3.6f)

Punch list §25 item 4.3.6f complete. TEXT ( c-addr u x y size color -- )
walks a UTF-8 byte string, decoding one codepoint at a time via
DECODE-UTF8, drawing each via DRAW-GLYPH, and accumulating the cursor
X by the glyph's em-advance scaled to pixels. Uses 2>R/2R> to stash
the DECODE-UTF8 remainder off the data stack while DRAW-GLYPH's args
are pushed.

Defined in font.4th, not fabric.4th, so its compiled DRAW-GLYPH call
binds to the real definition, not fabric.4th's 4.3.6b placeholder --
same early-binding constraint as DISPATCH-GLYPH itself.

Verified live: a string mixing ASCII, Latin-1 (degree sign), and
General Punctuation (em dash) renders correctly in one TEXT call with
proportional spacing, no overlap.

Three-arch acceptance boot clean, Stadium conservation unchanged.

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

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