feat(@projects): ✨ add stats screens design doc

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

.project/designs/stats-screens.md

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+# In-game Statistics Screens
+
+Civ-style statistics surfaced during a live game. Player can open at any turn to compare their civilization against rivals across multiple axes. Read-only views over per-turn snapshots the simulator already records for the AI's strategic evaluation.
+
+## Surfaces
+
+Five tabs in a single `Statistics` modal scene, opened from the HUD info button (or `F9`). Each tab is one full-bleed view, so opening the modal lands on the most-recently-viewed tab.
+
+| Tab | What it shows | Primary widget |
+|---|---|---|
+| **Demographics** | Single-turn snapshot of every clan: population, cities, army strength, gold, culture, tech count, score. Player's row highlighted; columns sortable. | Sortable table |
+| **Graphs** | Per-turn line graph; one line per known clan. Y-axis selector: score / population / cities / army / gold-per-turn / culture-per-turn / tech-count / land-area. X-axis is turn number. | Multi-line chart |
+| **Rankings** | Top-N leaderboard for the currently-selected metric. Reuses the Graphs Y-axis selector. Shows trend arrow vs. previous turn. | Ranked list |
+| **Replay** | Time-scrubber over the current game's turn history. Map preview + key-events ticker (city founded, war declared, wonder built, leader killed). Live-game version of the post-game replay (see [past-games-replays.md](past-games-replays.md)). | Map + scrubber + event log |
+| **Histories** | Per-clan chronicle: founding turn, wars fought (with outcomes), wonders built, eras entered, leaders. Tab through clans. | Timeline |
+
+## Visibility rules
+
+- A rival clan only appears in Demographics / Graphs / Rankings once the player has met them. Pre-contact rivals are absent (not greyed) — discovering them mid-game retroactively backfills their line on the graph from the contact turn forward only.
+- Espionage / scrying upgrades (post-Game-1) widen what's visible per rival; in Game 1 every met rival shows the full column.
+
+## Data source
+
+Each turn-end the simulator appends one `ClanStatSnapshot` row per clan to `GameHistory.snapshots: Vec<TurnSnapshot>`. Snapshots are the same data the strategic AI already reads for threat assessment — no new bookkeeping, just a UI projection.
+
+| Field | Type | Source crate |
+|---|---|---|
+| `turn` | `u32` | `mc-turn` |
+| `clan_id` | `ClanId` | `mc-core` |
+| `population` | `u32` | `mc-economy` |
+| `cities` | `u32` | `mc-economy` |
+| `army_strength` | `f32` | `mc-combat` (sum of unit power) |
+| `gold` | `i64`, `gold_per_turn` | `mc-economy` |
+| `culture_per_turn` | `f32` | `mc-economy` |
+| `tech_count` | `u32` | `mc-tech` |
+| `land_area` | `u32` (hexes owned) | `mc-economy` |
+| `score` | `f32` | `mc-score` (composite) |
+
+`GameHistory` is owned by `mc-replay` (new crate, see [past-games-replays.md](past-games-replays.md)) and is the same artefact serialized at game-end for the past-games archive.
+
+## Score formula
+
+Score is one composite number used for the Rankings default and for end-game ordering. Weights live in `public/games/age-of-dwarves/data/score.json` (Rail-2: no hardcoded weights). First pass:
+
+```
+score = w_pop * population
+      + w_cities * cities
+      + w_tech * tech_count
+      + w_culture * culture_total
+      + w_land * land_area
+      + w_wonders * wonder_count * 10
+      + w_military * army_strength
+```
+
+The exact weights are tuning data, not design — the design commitment is "one composite score, JSON-driven weights, recomputed every turn-end".
+
+## Source-of-truth pointers
+
+- Snapshot type + history container: `src/simulator/crates/mc-replay/src/snapshot.rs` (to be created)
+- Score formula data: `public/games/age-of-dwarves/data/score.json` (to be created)
+- Modal scene: `src/game/engine/scenes/statistics/statistics.gd` (to be created)
+- React mockup target: `app/src/pages/Statistics.tsx` (route `/stats`)
+
+## See also
+
+- [end-game-summary.md](end-game-summary.md) — terminal version of these stats
+- [past-games-replays.md](past-games-replays.md) — archive surface that consumes the same `GameHistory`