feat: add enum support to Explorer

[rasadregmi]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

Closes #605

This PR adds enum support to Explorer, which currently has no way to see TypeScript enums at all.

Because of that, curriculum tests have to assert enums with regular expressions. A concrete example is the Digital Pet Game lab:

https://github.com/freeCodeCamp/freeCodeCamp/blob/main/curriculum/challenges/english/blocks/lab-digital-pet-game/68c362b379059c388d3874f2.md

Eight assertions in that lab (lines 360-402) each check one member like this:

assert.match(code, /\s*enum\s+PetMood\s*{[\s*\w+,\s*]*HAPPY[\s*\w+,\s*]*}/);

The character class [\s*\w+,\s*] only allows word characters, commas and *, so this passes for HAPPY, but rejects the equally valid HAPPY = 'HAPPY', — the =, the quotes and the spaces around them all fall outside the class.

With enum support the same check becomes a single assertion:

const explorer = new Explorer(code);
assert.deepEqual(Object.keys(explorer.enums.PetMood.enumMembers), ["HAPPY"]);

Why this is better in practice:

• accepts any valid enum member, including HAPPY = 'HAPPY'
• no duplicated regex per member
• scope is handled for you, so an enum declared inside a function won't produce a false pass
• value exposes the initializer, so enumMembers.HAPPY.value.matches("'HAPPY'") works

Implementation notes:

• findMembers now returns EnumDeclaration.members; its return type is widened to include EnumMember, which does not extend ClassElement
• new enums and enumMembers accessors, mirroring classes and methods
• value returns an enum member's initializer, or an empty Explorer
• a new enumMember parse context so matches() works

That last one is required rather than incidental. An EnumMember is neither a TypeNode nor an Expression, so it falls through every existing CONTEXT_GUARDS entry to "source", where it gets compared against an ExpressionStatement — which never matches.

Regular, const and exported enums are all EnumDeclaration statements, so all three are found. Members are keyed with name.getText() rather than the (name as Identifier).text cast used elsewhere in the file, because ComputedPropertyName has no text property and would collapse every computed member onto a single bogus undefined key.

Tests cover regular/const/exported enums, initialized and uninitialized members, string, numeric and computed initializers, scope isolation, non-identifier member names, and the exact HAPPY = 'HAPPY' case the lab regex rejects. The new tests were confirmed to fail before the fix and pass after it.

pnpm test:unit (344 tests) and pnpm test:python (137 tests) pass, along with pnpm lint and pnpm build.

On documentation: I documented the new accessors using the same inline comment convention every other accessor in explorer.ts follows. I did not add a docs page because Explorer doesn't have one today — docs/ has no Explorer references at all and docs/javascript.md is a 3-line stub. Happy to add one if you'd prefer that, though it would mean a new file plus a SUMMARY.md nav entry.

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