v0.8.0

v0.8.0 — The Safe Core

Safety-focused release closing the highest-severity findings from the
0.7.7 product review.

Security:
- rt_exec no longer shells out (AOT + JIT both hardened).
- AOT linker flags allowlisted against [A-Za-z0-9_.+-]+.

Changed:
- rt_pow is overflow-checked; negative exponents abort.
- read_fd_to_string rebuilt to avoid arena realloc corruption.

Added:
- try_read_file / try_write_file return str ! str.
- hashmap_set_int / hashmap_get_int str→int variant.

See CHANGELOG.md for details.