- Created env.c/h: key=value store with ENV_MAX_VARS=32 entries per
process. Supports get, set, unset, and copy operations.
- Added env_block_t and cwd[128] fields to process_t struct.
- process_create() initializes CWD=/ by default.
- Fork inherits environment via memcpy of the entire process_t.
- Added SYS_GETENV (8) and SYS_SETENV (9) system calls.
- Created env-test user app that verifies: CWD default, set/get,
and inheritance across fork.
- Updated kernel.c to launch 'sh' as init process (for next task).
- Updated README.md to check off environment variables task.
Tested: env-test reads CWD=/, sets TEST=hello, reads it back,
forks child which inherits TEST=hello. All verified via QEMU.
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