Bounded search foundations and source-navigation recall

[TheCryptoDonkey]

Summary

• Restore bounded source-navigation recall with exported-name anchors and fair symbol selection.
• Add isolated SQLite and posting-page scale experiments, including a measured million-record ID-only tier.
• Add internal memory-store fixtures and fix Node Buffer copy isolation.
• Document core-first release gates, evidence, architectural boundaries and remaining work.
• Run navigation and scale regression checks in CI.

Verification

• 61 package tests and independent tarball smoke pass locally.
• Both unchanged token benchmark gates pass.
• 22 scale tests and the 10k posting probe pass.
• No public API, signed-format, package-version or production deployment changes. Synthetic plaintext experiments are not suitable for private repositories.

Delivery boundary

This ships the source milestone, not enterprise readiness or a new npm release.