[tyza66]

What

Fixes #1: vowel groups are now split on hiatus when a high vowel (i, u)
carries the stress, so rainha counts 3 (ra-i-nha) and fotografia
counts 5 (fo-to-gra-fi-a) instead of 2 and 4.

Why

HIATUS_MARKERS = "íú" only matched an accented high vowel in second
position, and neither i nor u is in STRONG. So the pair ai/ia never
split, and every unaccented word with a high-vowel hiatus was undercounted.

The fix

Portuguese decides hiatus versus diphthong by whether the high vowel carries
the stress, so the counter now locates the stressed vowel first
(stressed_vowel) and then breaks a vowel group when a high vowel is a
nucleus rather than a glide:

rule	example
a high vowel that carries the stress is a nucleus	ra-i-nha, fo-to-gra-fi-a, sa-í-de, ru-ím
a stressed high vowel before a strong vowel also splits	Ma-ri-a, po-e-si-a, a-tu-a
an unstressed high vowel after another vowel in the same group glides onto it, so the next vowel starts a new syllable	prai-a, chei-o, sa-iu
two strong vowels in a row are two nuclei (unchanged)	co-e-lho, le-ão

Three supporting changes came with it:

• vowel groups are now index ranges instead of strings, so the stress can be
  compared against a position inside the group;
• the silent u of que/gue/gui is dropped before counting;
• HIATUS_MARKERS is replaced by HIGH, STRESS_MARK and HIATUS_WORDS
  (the old constant is gone, since it no longer describes the rule).

Rising diphthongs are deliberately left alone: dia, rua, pai, caixa,
história, família, diabo, médio all keep their current counts, and
the existing 11 words in test_portuguese_syllables still pass unchanged.

Tests

test_portuguese_syllables gains the words from the issue plus guards on both
sides of the new rule, and a new test pins the silent-u behaviour. The suite
is 9 runs / 60 assertions, still dependency-free and green on Ruby 3.1 and 3.3.

I also diffed the new counter against the old one over a 318-word Portuguese
word list: 32 words move to the correct count, 0 regress.

Known limits

This stays a heuristic, and two classes of word are still wrong:

• Portuguese does not mark the stress of unaccented words, so the few common
  words where a high vowel is stressed instead of glided are listed in
  HIATUS_WORDS. That list is admittedly a stopgap; a real syllable
  dictionary or a stress model would replace it.
• Some pairs are lexical and cannot be told apart from the spelling:
  criança (cri-an-ça) versus caixa (cai-xa), diálogo (di-á-lo-go)
  versus diabo (dia-bo). Those are unchanged from before.

Happy to rework any of this if you'd rather scope it differently.

Disclosure

This PR was written with AI assistance. I used
Alpha to locate the root
cause, prototype the rule set against a 318-word Portuguese word list, and
draft the patch and this description. Every change was reviewed by me before
committing, and I verified the diff is a strict improvement over the previous
counter with no regressions.

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