libghostty now builds as a static library

*CMake and Zig tooling mature enough to ship the VT library in multiple forms.*

@mitchellh merged #11732 to add static library support alongside the existing dynamic build. This follows weeks of infrastructure work: CMake support landed in #11700, Zig optimization flags for release builds in #11707, and CI validation in #11703. Static linking reduces runtime dependencies for consumers of libghostty-vt, particularly useful for embedded terminal implementations like ghostling.

VT decoder state now persists across vt_write calls

*Streaming parsers no longer reset mid-sequence when input arrives in fragments.*

The VT state machine in libghostty-vt previously lost context between separate write operations. #11728 preserves decoder state across boundaries — critical for any consumer receiving escape sequences in chunks rather than complete messages. This is a correctness fix disguised as infrastructure work; parsers that can't hold state across I/O boundaries produce corrupted output or drop sequences entirely.

libghostty C API expands with build info and cell inspection

*Consumers can now query renderer state and terminal grid contents directly from C.*

#11725 adds a ghostty_build_info API for querying build configuration, while #11676 provides grid point and cell inspection — the low-level terminal data structs that screen readers and clipboard handlers need. Together with #11664's render state API, the C interface now exposes enough of the terminal's internals that alternative UIs (like ghostling) and accessibility tools can work directly with rendered output without reimplementing parsing.