Phase 1: OSS-Fuzz submission (continuous fuzzing)

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Part of Phase 1 — Hardening & modernization (ROADMAP.md).

Phase 0 landed a libFuzzer harness + seed corpus under fuzz/. OSS-Fuzz gives free, continuous, coverage-guided fuzzing for OSS:

• Write the OSS-Fuzz build.sh / project config for the fuzz_parse target.
• Submit the project integration PR to google/oss-fuzz.
• Wire up crash/coverage reporting.

Builds on the existing fuzz/ harness.