Fix SCSS analysis failing on same-line prop:value declarations and consecutive semicolons

[cscheid]

Closes #14687, closes #11703.

Problem

cssVarsBlock (the SCSS static analysis that exports theme colors as --quarto-scss-export-* CSS variables) parses the assembled SCSS bundle with the brittle third-party scss-parser@1.0.6. Two shapes of valid SCSS (Dart Sass compiles both fine) made it throw SCSSParsingError: Expecting punctuation: "}", silently dropping the color export (render still exits 0):

1. SCSS analysis fails on same-line declarations with no space after colon (.example {width:100px;}) #14687 — a declaration on the same line as the opening brace, with no space after the colon and a non-identifier value, e.g. .example {width:100px;}. The existing colon-spacing workaround in src/core/sass/analyzer/parse.ts was anchored at line start, so same-line declarations escaped it. (Standalone reproduction: https://github.com/gigamonkey/quarto-scss-bug — thanks @gigamonkey.)
2. SCSS fails to parse #11703 — consecutive semicolons inside a block (an empty statement), e.g. max-height: 100% !important;;, even when the semicolons are separated by whitespace or newlines. Diagnosed by bisecting the personal.scss attached to that issue; with the ;; collapsed, the whole file parses.

Fix

Two more targeted text rewrites in src/core/sass/analyzer/parse.ts, alongside the six existing workarounds of the same kind (these rewrites only affect the analysis copy of the SCSS, never what Dart Sass compiles):

• /([{;]\s*[A-Za-z0-9-]+):([^ \n])/g → "$1: $2" — same-line sibling of the existing line-start colon fixup.
• /;[\s;]*;/g → ";" — collapse each run of semicolons into one.

Tests

• New unit test tests/unit/scss-analyzer-parse.test.ts runs 21 valid-but-tricky SCSS shapes through getSassAst plus a cssVarsBlock color-export check (verified to fail without the fixes).
• New smoke-all regression tests tests/docs/smoke-all/2026/07/14/issue-14687.qmd and issue-11703.qmd, asserting the --quarto-scss-export-* variables survive and no warnings are emitted.
• Existing SCSS-analysis regression tests (add new scss-parser workaround #12338 corpus, Error adding css vars block SCSSParsingError #14065 unicode tests) still pass.
• End-to-end: the gigamonkey reproduction renders cleanly (no error, no _quarto_internal_scss_error.scss dump, export block present in the compiled CSS), and SCSS fails to parse #11703's original personal.scss now parses through getSassAst.

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