Add a new `isTerminal` static method to the Stdin class that returns `true` when
stdin is connected to a TTY (interactive terminal) and `false` when input comes
from a pipe. Implementation uses libuv's `uv_guess_handle` to check the stdin
descriptor. Includes documentation, foreign method declaration, module
registration, and a test expecting `false` since tests run non-interactively.
Add foreign static getter `isRaw` and setter `isRaw=(value)` to the Stdin class, backed by a new `isStdinRaw` boolean flag and `uv_tty_set_mode` calls. The getter returns the current raw mode state, while the setter initializes the stdin stream if needed and applies raw or normal mode only when stdin is a TTY. Also includes a test file verifying default false, reading bytes in normal mode, enabling raw mode, and reading subsequent bytes.
Implement a new `readByte()` static method on the `Stdin` class that reads one byte from standard input, blocking the current fiber until a byte is received. The method returns the byte value as a number or `null` if stdin is closed.
Refactor the internal buffering mechanism by introducing a shared `read_()` helper method that both `readByte()` and `readLine()` use, replacing the previous per-method buffering logic. The `readByte()` implementation peels off the first byte from the internal `__buffered` string using `bytes[0]` and slicing.
Add two test files: `read_byte.wren` verifying byte-by-byte reading of "first" and "second" input lines, and `read_byte_eof.wren` confirming that reading after stdin is closed returns the expected error message.
Restructure the documentation hierarchy to prepare for documenting additional built-in modules. Move all core library documentation from `doc/site/core/` to `doc/site/modules/core/`, rename `modules.markdown` to `modularity.markdown`, remove `^category` metadata lines from all affected pages, update cross-reference links to use relative paths under the new structure, and add a TODO placeholder to the Class class page.
