Task: Integrate Next and Go architecture design into main

Identity

Integrate the approved Next.js frontend plus Go backend design and the explicit implementation progress into canonical project memory.
Preserve the distinction between the implemented ACK-001 topology and the accepted-but-unimplemented ADR-003 target.
Merge documentation only; exclude all interrupted Go, Docker, Compose, ACK, package, SQL, and application drafts.

The user explicitly requested design and progress documentation only, merged to main.
Promote the human-confirmed architecture without claiming that the Go backend exists.
Retain RDS-001 and RDS-002; mark ACK-001 as current transition state until implementation and cutover.
Preserve the occupied main worktree's unrelated untracked runtime configuration task record.

Added ADR-003 as an accepted target with implementation pending.
Added current-versus-target sections to system overview, module map, and data flow.
Updated current state, task history, decision index, and commitments with explicit not-implemented progress.
Integrated the feature task record and detailed architecture proposal.
No runtime, application, database, build, package, or deployment file changed.
The first drift check correctly reported that source task-owned records were introduced after this task's recorded base. The prepared canonical state will be committed as a fixed read-only base, this integration lock released, and a fresh Integration Gate task will perform final validation without treating source records as integration-owned edits.

Source documentation commit ed60e74 was cherry-picked as 4485899 onto the integration base.
Source feature drift check passed before completion.
Canonical changes preserve current ACK-001 facts while recording ADR-003 as future target.
Initial integration drift check: blocked on source-record base ordering, not on document content.
A fresh Integration Gate based on the fixed source/canonical candidate commit is required before merging main.

Implement ADR-003 in a separate future task only after compatibility tests are executable.
Live RDS/ACK/OSS/provider validation remains outside this documentation-only integration.