chore: add Apache-2.0 SPDX license headers

[tnunamak]

Adds Apache-2.0 SPDX headers to 304 selected first-party source files.

• Added: 296 JavaScript or TypeScript, 4 shell, and 4 CSS headers; preserved 34 shebangs.
• Skipped: 48 vendor, bundled connector, third-party icon or UI primitive, generated, and fixture files; JSON, lock, and configuration data were excluded.
• Verified: typecheck, build, standalone runner harnesses, and git diff --check pass. Lint, formatting, and aggregate Vitest failures reproduce on main because of existing tool configuration and test discovery issues.