feat(core): report patch lines that do not parse

Fixes #420

A line that starts with { and has an "op" key but fails parseSpecStreamLine — a truncated patch, for example — was handled two ways and neither reported it: inside a ```spec fence it was dropped silently, outside one it was shown as prose. When the token limit cuts a replace short the spec stays valid, so a validator sees nothing wrong and the user sees an edit that never happened.

Change

packages/core/src/types.ts

• onInvalid?(line) on MixedStreamCallbacks and on a new JsonRenderTransformOptions passed to createJsonRenderTransform(options?). It fires only for patch-shaped lines ({ … "op":), so ordinary prose that starts with { is unaffected.
• dropInvalidPatches?: boolean on both: a patch-shaped line outside a fence is then dropped instead of streamed as text. Inside a fence such a line is always dropped, as before.
• createMixedStreamParser(callbacks, options?) keeps its existing call shape; the second argument is optional.
• Exported MixedStreamParserOptions and JsonRenderTransformOptions from the package.

Tests

packages/core/src/types.test.ts

• Mixed parser: reports an unparsable patch inside a fence (no text, no patch); reports one outside a fence and still emits it as text by default; drops it outside a fence with dropInvalidPatches: true; leaves {not a patch} alone.
• Transform: the same inside-fence and outside-fence cases over real chunks, including the dropped-line text assertion.

Verified: pnpm exec vitest run packages/core/src/types.test.ts -> 131 passed; with types.ts reverted, the six new tests fail. tsc -p packages/core/tsconfig.check.json exits 0 and prettier --check is clean.