microlisp 0.1.4

Fourth post-release iteration. Five findings from a fresh cold
reviewer, all landed.

See CHANGELOG.md for the full inventory.

Added

• MICROLISP_ERR_EQUAL_DEPTH + microlisp_options::max_equal_depth
  (default 1024). equal? and eqv? walked pair-car chains
  recursively without a bound; two 500k-deep nested structures
  used to SEGFAULT. Same depth-guard pattern as the printer in
  v0.1.3.

Fixed

• equal? / eqv? no longer crash on deeply-nested
  structures. ASan-confirmed clean.
• microlisp_repl now honors its out_file contract.
  display, write, newline route through a state->output
  field that the REPL swaps to out_file for its duration,
  instead of writing directly to stdout.
• Allocator alignment contract documented and enforced.
  microlisp_state_create checks the first allocation rather
  than letting a misaligned arena silently corrupt tagged
  values on the next GC.
• microlisp no longer prints the prompt on piped stdin.
  The comment said this was intended; the code shipped without
  the isatty check until now.
• scripts/coverage.sh owns reset/test/capture/enforce.
  Stale .gcda files used to merge with new counters, libgcov
  spammed stderr, and a CLI regex test broke. The script now
  deletes .gcda before running ctest.

Source tarball

A deterministic tarball is attached: `microlisp-0.1.4.tar.gz`
plus SHA-256 checksum.

```sh
sha256sum -c microlisp-0.1.4.tar.gz.sha256
tar xzf microlisp-0.1.4.tar.gz
cd microlisp-0.1.4
cmake --preset release
cmake --build --preset release
ctest --test-dir build/release --output-on-failure
```