chore(release): bump version to 0.7.3

[indigo423]

Release bump for v0.7.3.

Bumps package.json / package-lock.json to 0.7.3 so the release workflow's version guard matches the v0.7.3 tag. Merge commit will be tagged per RELEASING.md.

What's in v0.7.3

• Security fix: resolved three high-severity npm audit advisories that were blocking CI — next → 16.2.11, overrides forcing sharp ≥0.35.0 (libvips CVEs) and immutable ≥5.1.8 (DoS) (fix(deps): resolve high-severity npm audit vulns blocking CI #123).
• Routine dependency updates (chore(deps): Bump actions/setup-node from 6.4.0 to 7.0.0 #113, chore(deps): Bump prettier from 3.9.4 to 3.9.5 #114, chore(deps): Bump eslint from 9.39.4 to 9.39.5 #116, chore(deps): Bump actions/checkout from 7.0.0 to 7.0.1 #117, chore(deps): Bump @fontsource/press-start-2p from 5.2.7 to 5.3.0 #118, chore(deps): Bump prettier from 3.9.5 to 3.9.6 #120, chore(deps): Bump markdown-to-jsx from 9.8.2 to 9.9.0 #121, chore(deps): Bump react-dom from 19.2.7 to 19.2.8 #122).

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