Home ABI: diff the newer Home revision without silently repinning

Parent: #163 Depends on: #165

The local Home checkout advanced from the supported 7ed99c0 profile to 5e829ad while implementation was in progress. Treat it as a new candidate profile.

Acceptance:

• Generate a source/signature/classification diff against home-private-7ed99c0.
• Report added, removed, and changed declarations and calling conventions.
• Decide explicitly whether to support both revisions or supersede the older profile.
• If supported, check in a separate revision ID, hashes, inventory, and compile-link-runtime evidence.
• Keep the existing profile immutable and continue rejecting mismatched revisions until the new profile is complete.

Completed in aa11884 and documented in 66f2871.

The full packages/runtime/src/jsc revision diff is empty. home-private-5e829ad is a separate explicit alias whose audit verifies all 58 hashes and all 448 declaration locations, signatures, classifications, and calling conventions against the immutable 7ed99c0 inventory. The manifest reports 0 added, 0 removed, 0 changed, and 0 calling-convention changes. The 4-symbol compile-link-runtime fixture passes against the newer checkout.