[jstet]

Fixes #218.

LimeSurvey's `regexMatch(pattern, input)` takes the pattern first and needs it delimited (`/…/`). We emitted `regexMatch(self, 'pat')`, so the constraint was wrong for every input. Checked against the LimeSurvey source: PHP `exprmgr_regexMatch` runs `preg_match($pattern . 'u', $input)`, and JS `LEMregexMatch` strips `/…/flags` before `RegExp.test`.

• Order and delimiters: `regex(x, 'pat')` becomes `regexMatch('/pat/', x)`. A `/` in the pattern is escaped as `\/` (not already-escaped ones). The quote style of the XPath literal is kept; quotes need nothing else because XPath has no escapes.
• Anchoring: ODK `regex()` matches the whole value, while both LimeSurvey implementations search anywhere in it. So an unanchored pattern is wrapped as `^(?:pat)$`; a pattern that already starts with `^` and ends with an unescaped `$` (and has no `|`) is left alone. Without this, `regex(., '[0-9]{5}')` would accept `abc12345xyz`. A computed (non-literal) pattern is delimited and anchored at run time by string concatenation.
• Escape hatch: an author-written `regexMatch("pat", .)` in a constraint gets delimiters (and `/` escaping) but no anchoring, as it is already LimeSurvey syntax; an already delimited pattern is kept.
• Reverse (lstsv2xlsform): `regexMatch('/pat/', x)` reads back to `regex(x, 'pat')`, undoing the delimiters, the `/` escaping and the `^(?:…)$` wrapper. The old field-first `regexMatch(x, 'pat')` is still accepted. LimeSurvey-native unanchored patterns come back unchanged (so ODK will match the whole value), and flags such as `/pat/i` have no ODK form and are kept as text. The README's former known loss 7 (argument order) is replaced accordingly.
• `convention:logicMapping` documents the mapping; `src/generated/` is regenerated.

Before:
```
regex(., '^[0-9]{5}$') -> regexMatch(self, '^[0-9]{5}$')
regex(., '[0-9]{5}') -> regexMatch(self, '[0-9]{5}')
```

After:
```
regex(., '^[0-9]{5}$') -> regexMatch('/^[0-9]{5}$/', self)
regex(., '[0-9]{5}') -> regexMatch('/^(?:[0-9]{5})$/', self)
```

The `testB` snapshot changed only in its two email-regex constraint rows (blessed and diff inspected). Not run against a live LimeSurvey here; the issue's live valid/invalid test is still worth doing.

Tests

• Forward: delimiters, anchoring, alternation grouping, `/` escaping, quote styles, escaped `$`, computed pattern, escape-hatch delimiting.
• Reverse: delimited, anchored, escaped, native-unanchored, flags, and the old field-first form; forward-then-reverse restores the original XPath.
• `npm test`: 108 files and 1794 tests pass (1773 before). `npm run validate` (lint, types, format, knip, dup, arch, markdownlint) is clean.

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