docs: replace the level ladder with the Atlas

[colorpulse6]

Summary

• define the long-horizon civilization frontier and its continuity safeguards
• retire numbered W1-W8 progression from the canonical galaxy while preserving existing missions as located operations
• make continuous projected coordinates, hierarchical Atlas zoom, free plotting, deterministic spatial cells, and knowledge-limited navigation authoritative
• insert G0 Atlas before M3-M5 as the next systemic substrate while M2 art continues in parallel
• define the G0 vertical slice, fresh galaxy-save boundary, atomic travel journal, legacy adapters, accessibility, and acceptance gates
• add the 14-slice, 110-step test-first implementation plan with exact file ownership, serialized contracts, versioned G0 coordinates/economy, operation payloads, interruption closure, DevPanel fixtures, and production playtest gates

Why

The current eight-world canvas arc is an implementation wrapper, not a sufficient structure for an explorable galaxy spanning colonies, generations, travel time, and persistent history. Later systems should attach to stable coordinates and operation identities before they create more numeric-world dependencies.

The implementation plan removes the remaining build-time ambiguity before runtime work begins: legacy and galaxy histories have separate authority, every generated coordinate is reproducible, travel can resume safely from every saved state, and the existing shooter, Kepler, Ashfall, colony-cycle, and mission-delivery systems have explicit adapter boundaries.

Verification

• independent spec review completed and all implementation-significant findings resolved
• three-pass independent implementation-plan review completed; every reported blocker was resolved in the document
• complete generation identity and fail-closed unsupported-version behavior are specified and tested
• travel commit, interruption closure, blind arrival, and emergency retreat are checkpoint-idempotent across double-confirm and reload
• legacy progression cannot gate or leak into canonical galaxy runs, and the plan includes an end-to-end legacy mission regression playtest
• pointer, touch, keyboard, DOM-only navigation, and all four conceptual Atlas view levels have acceptance criteria
• git diff --cached --check and committed-diff check passed
• document authority and supersession links checked
• docs-only change; runtime behavior unchanged

Review focus

Please review the G0 boundary, versioned content/economy table, fresh-save policy, continuous-coordinate model, operation adapters, travel transaction/closure contract, task ordering, and revised roadmap order.

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