Clamp editor trace lookup position

[liurenfeng94-ops]

Fixes an editor-to-trace navigation edge case.

gotoTracePosition subtracts one from the editor offset for normal cursor positions before filtering the trace tree. At the beginning of a file that produced -1, which makes the trace filter behave like no position was supplied. This clamps the computed trace position at zero.

Validation:

• pnpm vitest run test/editor-trace-position.test.ts
• pnpm vitest run
• pnpm typecheck
• pnpm exec eslint .
• pnpm build

[github-actions]

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