Add NEWS.md, rename LICENSE.md to LICENSE, add utility tests

Issue #3: Create NEWS.md documenting version 0.3.2 changes for CRAN
compliance — R requires a news file at submission.

Issue #4: Rename LICENSE.md -> LICENSE per R packaging conventions so the
LGPL-3 license ships correctly in built tarballs. Updated .Rbuildignore to
remove the ^LICENSE\.md$ exclusion and add ^NEWS\.md$.

Issue #5: Add comprehensive test coverage for three previously untested
exported utility functions in tests/testthat/test_utils.R:
  - postcode_lookup(): returns correct abbreviations, handles DC/Puerto Rico,
    is vectorized, returns NA for unknown states, matches all state.name entries
  - race_short_names(): maps all NCES categories correctly, coerces factors to
    character, passes through unrecognized values unchanged, handles empty input,
    and exhaustively verifies against a reference implementation across every
    variant string the function accepts
  - get_fips(): errors gracefully when tidycensus is absent with an informative
    message; returns correct FIPS codes (MT=30, CA=06) when installed

All 21 new test blocks pass. The pre-existing na_sum quiet=TRUE failure in
test_utils.R line 63 was not introduced by these changes.

NEWS.md

@@ -0,0 +1,16 @@
+# civilytics 0.3.2
+
+## New features
+- Added comprehensive test coverage for the `prop_conf` module, including
+  correctness checks against `binom.test()` for Clopper-Pearson intervals and
+  formula-based verification for Wald and Agresti-Coull intervals.
+
+## Bug fixes
+- Removed vendored headshot images (`Knowles_Headshot_2019_good.jpg`,
+  `Knowles_Headshot_2019_prisma.jpg`) from `inst/img/` to prevent personal
+  photos from being distributed with the package. The `plot_jpeg()` example
+  now references a generic placeholder path instead of a specific headshot.
+
+## Internal
+- Renamed `LICENSE.md` to `LICENSE` for R packaging convention compliance so
+  that the LGPL-3 license ships correctly with built tarballs.