Add README logo, status badges, and measured Rust coverage

[dweekly]

Add the existing moon-and-magnifying-glass logo to the README, followed by linked CI, Codecov, latest-release, and MIT OR Apache-2.0 badges.

A separate path-filtered workflow measures Linux line coverage using cargo-llvm-cov. It installs the required official Lua compilers and instruments both the workspace test suite and the CLI launched by subprocess tests. The report excludes the oracle tooling crate while still running its tests. Reports are retained as Actions artifacts and uploaded through codecov/codecov-action@v5 with CODECOV_TOKEN.

Containment tests deliberately terminate child processes, which can interrupt coverage writes. LLVM warns about invalid profiles and retains valid ones; an invalid-only report still fails. Tests and their pass/fail criteria are unchanged.

Validation:

• GitHub README rendering visually checked; logo and badge links resolve.
• actionlint, shell syntax, and diff checks passed.
• Coverage workflow passed and Codecov accepted the upload: 18,400 of 21,784 lines hit (84.47%) across 60 product source files, including positive CLI/core/analysis counts.
• A local positive/negative profile-merge check accepted valid-plus-truncated profiles and rejected invalid-only input.
• Existing Linux/macOS CI supplies aggregate correctness, official compiler, fuzz, and packaging checks.

Includes current 0.3.0 content from main. Coverage is a development metric, not a supported-target or semantic-correctness claim.

[codecov-commenter]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered ☂️