Docs/ac 0001 v0 governance

[danieldilly]

Summary

This PR establishes the governance foundation for AC-0001 (v0 two-client multiplayer slice):

• Add/update Constitution: invariants (INV-0001 through INV-0006), domain model concepts, acceptance/kill criteria
• Refactor ADR-0001 from three-plane to authoritative multiplayer architecture
• Update ADRs 0002-0005 with Constitution ID references and cross-links
• Add FS-0007 spec for v0 two-client multiplayer slice (Draft status)
• Update documentation (handbook, repo-map, README, copilot-instructions) to reflect new governance structure

Trace Block

Issue: #7
Spec: docs/specs/FS-TBD-v0-multiplayer-slice.md
Constitution: INV-0001, INV-0002, INV-0003, INV-0004, INV-0005, INV-0006, DM-0001, DM-0002, DM-0003, DM-0005, DM-0006, DM-0011, DM-0014, AC-0001, KC-0001, KC-0002
ADRs: ADR-0001, ADR-0002, ADR-0003, ADR-0004, ADR-0005

Files Changed

Constitution:

• docs/constitution/invariants.md - Added INV-0001 through INV-0006
• docs/constitution/domain-model.md - Added domain concepts
• docs/constitution/acceptance-kill.md - Added AC-0001, KC-0001, KC-0002
• docs/constitution/id-catalog.json - Machine-readable ID catalog
• docs/constitution/id-index.md - Generated ID index
• docs/constitution/id-index-by-tag.md - Generated tag index
• docs/constitution/tag-taxonomy.md - Tag system

ADRs:

• docs/adr/0001-authoritative-multiplayer-architecture.md - NEW: Replaces three-plane architecture
• docs/adr/0002-deterministic-simulation.md - Updated with Constitution IDs
• docs/adr/0003-fixed-timestep-simulation.md - Updated with Constitution IDs
• docs/adr/0004-server-authoritative-architecture.md - Updated with Constitution IDs
• docs/adr/0005-v0-networking-architecture.md - Updated with Constitution IDs

Spec:

• docs/specs/FS-TBD-v0-multiplayer-slice.md - NEW: Draft spec for AC-0001

Documentation:

• .github/copilot-instructions.md - Updated with Constitution ID references
• README.md - Updated with governance structure
• docs/handbook.md - Updated
• docs/repo-map.md - Updated

Determinism / Simulation Impact

• This PR changes simulation-plane logic
  • No simulation code changes. This is pure governance/documentation. Establishes invariants and architecture that will constrain future implementation.

Verification

What you ran and what passed:

• just ids - Constitution ID validation passed
• just ids-gen - Generated indices committed
• just ci - To be run (requires spec-lint to pass with issue AC-0001: v0 Two-Client Multiplayer Slice #7)
• just spec-lint - To be verified with updated spec

Risk / Notes

Governance-only PR:

• No implementation code in this PR
• Establishes Constitution invariants (INV-0001 through INV-0006) that constrain future work
• ADR-0001 refactored to focus on authoritative multiplayer (removed "three-plane" framing)
• Spec status is Draft - requires approval before implementation begins
• Note: Spec filename still has "TBD" prefix - should be renamed to FS-0007 after merge

Follow-up work:

• Rename spec file from FS-TBD-v0-multiplayer-slice.md to FS-0007-v0-multiplayer-slice.md after issue number confirmed
• Spec review and approval (status: Draft → Approved)
• Implementation PR (separate, after spec approval)

Checklist

• Trace block is complete and accurate
• This PR stays within Constitution invariants (establishes them, doesn't weaken)
• No new dependencies added
• Spec exists (docs/specs/FS-TBD-v0-multiplayer-slice.md, Draft status)
• Constitution changes: just ids-gen run and outputs committed