Add info on statuses

STATUSES.md

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+# Game & Purchase Status Definitions
+
+## Game Statuses
+
+Games have a `status` field with the following values:
+
+| Status | Code | Description |
+|--------|------|-------------|
+| **Unplayed** | `u` | Game was purchased but never played |
+| **Played** | `p` | Game was played but not yet finished |
+| **Finished** | `f` | Game has been completed |
+| **Retired** | `r` | Game was intentionally retired (e.g., no longer accessible, collector's item) |
+| **Abandoned** | `a` | Game was played but the user gave up on it |
+
+**Setting game status:**
+- Users explicitly set game status via the UI (finish/drop purchase buttons, status change form)
+- Status changes are tracked in `GameStatusChange` model
+- Refunding a purchase always marks its games as abandoned
+
+---
+
+## Purchase-Level Status Concepts
+
+These concepts determine whether a purchase appears in the "unfinished" or "dropped" lists in stats views.
+
+### Finished
+
+A purchase is considered **finished** when:
+
+```
+Game.status == "f" OR Purchase.games.* has a PlayEvent with an ended date
+```
+
+Either signal indicates the game is complete:
+- **Explicit**: User marked the game as finished (`Game.status = "f"`)
+- **Implicit**: A PlayEvent exists with `ended` date set (data-driven)
+
+This uses **OR** logic during a transition period. Later, these signals should be kept in sync so only one source of truth is needed.
+
+### Dropped
+
+A purchase is considered **dropped** when:
+
+```
+Game.status == "a" OR Purchase.date_refunded IS NOT NULL
+```
+
+Either signal indicates the user no longer has an active interest in the game:
+- **Explicit**: User marked the game as abandoned (`Game.status = "a"`)
+- **Implicit**: User refunded the purchase (which automatically sets games to abandoned)
+
+Note: Refunding a purchase always marks its games as abandoned. There is no option to refund without abandoning.
+
+---
+
+## Unfinished vs. Dropped
+
+The stats views categorize purchases into **unfinished** and **dropped** lists.
+
+### Unfinished
+
+A purchase is **unfinished** when:
+1. It was purchased in the relevant time period (this year for yearly stats, all time for all-time stats)
+2. It was NOT refunded (only counts toward unfinished/backlog)
+3. It is NOT finished (per the finished definition above)
+4. It is NOT dropped (per the dropped definition above)
+5. It is NOT infinite (subscription, etc.)
+6. It IS a game or DLC (not season passes or battle passes)
+
+**Unfinished = Active backlog** — games the user may still play.
+
+### Dropped
+
+A purchase is **dropped** when:
+1. It was purchased in the relevant time period
+2. It is NOT finished (per the finished definition above)
+3. It matches at least one dropped signal (per the dropped definition above)
+4. It is NOT infinite
+5. It IS a game or DLC
+
+**Dropped = Terminal state** — games the user has given up on or refunded.
+
+### Summary Table
+
+| Category | Includes Refunded? | Key Condition |
+|----------|-------------------|---------------|
+| **Unfinished** | No | NOT finished, NOT dropped |
+| **Dropped** | Yes | Finished OR Abandoned/Retired |
+| **Refunded** | Yes | `date_refunded IS NOT NULL` |
+| **Infinite** | Yes | `infinite = True` |
+
+---
+
+## Query Patterns
+
+### Checking if a game is finished
+
+```python
+game.finished()  # Returns True if status="f" or has PlayEvent with ended date
+```
+
+### Checking if a game is abandoned
+
+```python
+game.abandoned()  # Returns True if status="a"
+```
+
+### Getting finished purchases
+
+```python
+Purchase.objects.finished()  # All purchases where games are finished
+```
+
+### Getting dropped purchases
+
+```python
+Purchase.objects.dropped()  # All purchases that are abandoned or refunded
+```
+
+---
+
+## Transition State
+
+The system uses **OR logic** for both finished and dropped to catch any mismatch between explicit user actions and data signals:
+
+- **Finished**: `status="f" OR PlayEvent.ended`
+- **Dropped**: `status="a" OR date_refunded`
+
+This bridges the gap between the old model (where `date_finished` and `date_dropped` were on the Purchase model) and the new model (where `Game.status` and `PlayEvent` are the sources of truth).
+
+**Future:** These signals should be kept in sync. For example:
+- Setting `Game.status = "f"` should create a PlayEvent with `ended` date
+- When the sync is reliable, the OR can be simplified to a single check
+
+Note: Refunding a purchase always automatically sets its games' status to Abandoned. This is not optional — there is no way to refund without abandoning.
+
+---
+
+## Edge Cases
+
+### Unplayed games
+- Unplayed games (`status="u"`) are considered **unfinished**, not dropped
+- They appear in the unfinished/backlog list since they are still games the user may play
+- Unplayed games that are refunded DO count as **dropped** (refund signal overrides)
+
+### Multiple games per purchase
+- A purchase can have multiple games via `Purchase.games` (many-to-many)
+- A purchase is finished if ANY of its games is finished
+- A purchase is dropped if ANY of its games is abandoned OR the purchase itself is refunded
+
+### PlayEvents without ended date
+- A PlayEvent with `started` but no `ended` does NOT count as finished
+- This represents a game that was started but not completed
+
+### Retired games
+- Retired games (`status="r"`) are considered **dropped**
+- Retirement is for games the user intentionally removed from their collection (collector's items, no longer accessible, etc.)