Add basic semantic PHP support

[coandco]

Summary

Added basic semantic PHP parsing.

Changes

• Modified types.rs to add .php and .inc files
• Added PHP nodes to is_semantic_node and is_comment_node in parser.rs
• Added .inc to the list of general filetypes gotten in src/config/constants.ts
• Wrote some PHP parse tests in tests/native.test.ts
• Updated documentation to reflect the new PHP support

Testing

How were these changes tested?

• Unit tests added/updated
• Manual testing performed
• Build passes (npm run build)
• Typecheck passes (npm run typecheck)
• Tests pass (npm run test:run)
• Lint passes (npm run lint)

Release Labels

• Added at least one release category label (feature, bug, performance, documentation, dependencies, refactor, test, chore, or skip-changelog)
• Added at most one semver label (semver:major, semver:minor, semver:patch) when needed

Related Issues

Fixes #34

[Helweg]

Validated locally on the PR branch.

• npm run build passed
• npm run typecheck passed
• npm run lint passed
• cargo test passed
• npm run test:run passed on a clean rerun

The change set matches the repo's documented scope for basic PHP semantic parsing support. PHP call-graph support remains out of scope for this PR and can follow separately.