Adds the consolidated, authoritative record for the 64MB memory
upgrade and N_SLOTS=8 investigation (real datasheet family comparison,
RTL changes, both timing fixes with real P&R data, honest N=8 clock-
closure status, real DigiKey availability for the frozen part).
Marks HARDWARE_FREEZE.md/MEMORY_ARCHITECTURE.md/PRE_PCB_VERIFICATION.md/
PRE_PCB_CLOSURE_4POINT.md's own SDRAM-specific sections as superseded
(they describe the previous 8MB AS4C4M16SA-6TIN part) with pointers to
the new document, rather than rewriting each individually.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013xXuuRUWZScuo1DeYJxs3v
micheleandClaude Sonnet 5
a20f1ecd73