fix: treat SoundEx initial characters literally

[ryanchou1994]

Fixes #541

Proposed Changes

• Compare the initial SoundEx code directly when removing duplicate initial consonant sounds. Building a regular expression from the first character can throw for inputs such as [foo], (foo), and *foo, or remove the wrong code for .foo.
• Add Jasmine regressions for those inputs and controls for empty input, Pfister, and the example with literal backticks.

Validation

• The new regressions fail on the original implementation: 20 SoundEx specs, 4 failures. With the fix, all 20 pass on macOS and Linux.
• All 863 unit specs pass on both platforms, along with the TypeScript test build, ESM build, and TypeScript lint. StandardJS and a duplication check of the two changed files also pass.
• The existing ESM smoke test and 16 assertions through the actual CommonJS and built ESM exports pass on both platforms.
• Tests ran with isolated configuration; Linux verification used a container with networking disabled. The IO suite and combined coverage command were not run because they require database services.

Checklist before merging

• Added Jasmine tests
• Updates TypeScipt index.d.ts files — not applicable; public signatures are unchanged.

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