Home ABI: generate the pinned private declaration inventory

Parent: #163

Establish the exact source-level private ABI denominator before implementing shims.

Acceptance:

• Pin Home revision 7ed99c0 and every JSC source file containing an extern declaration.
• Use a comment/string-aware scanner to capture every extern fn name, normalized signature, source location, source digest, and effective calling convention.
• Classify public-C overlap, platform imports, and private-JSC symbols with zero unclassified entries.
• Fail on revision, source, signature, duplicate-conflict, or classification drift.
• Publish exact totals and keep this inventory explicitly non-implementing; completion remains gated by #163.

Completed in 20228d6 and documented in 4ae1d42.

The pinned revision audit reports 448 unique symbols across 58 hashed source files: 432 private-JSC pending under #163, 15 completed public-C overlaps, and 1 external platform import. Every entry records its normalized declaration and digest, source/line, classification/status, and calling convention. There are zero duplicate and zero unclassified symbols. The live Home revision/source/signature comparison passes.