fix: export Key, KeyAction, Mods, DirtyState as runtime values

[oneilltomhq]

Problem

Fixes #129

lib/index.ts exports Key, KeyAction, and Mods as type-only (line 75), which strips their runtime values from the JS bundle. Consumers who do:

import { Key, KeyAction, Mods } from 'ghostty-web';

get undefined at runtime, even though the .d.ts declares them as real enums. This makes it impossible to construct a KeyEvent for KeyEncoder.encode() without manually duplicating the enum values.

Additionally, DirtyState (defined in types.ts, re-exported from ghostty.ts) is never included in index.ts, so it is not part of the public API.

CellFlags and KeyEncoderOption are already exported correctly as values — these four are the only ones affected.

Fix

• Changed Key, KeyAction, Mods from export type { ... } to export { ... } so they appear as runtime values in the bundle.
• Added DirtyState to the re-export from ./ghostty, alongside the existing CellFlags and KeyEncoderOption.

Verification

• tsc --noEmit passes
• biome check passes
• vite build succeeds
• All four enums confirmed as named exports in dist/ghostty-web.js
• .d.ts still declares all six enums correctly
• Test suite results identical to main (38 pass, 290 fail — the failures are a pre-existing happy-dom WASM fetch issue unrelated to this change)