docs(spec): add OperatorFilter.where() ergonomic constructor

Adds a Django-.filter()-style where(**lookups) classmethod (Component 1b)
to issue #56 spec. Additive: keeps the typed explicit constructor intact.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RF5L4HtbcykTfY9YUYGds3

docs/superpowers/specs/2026-06-21-issue-56-programmatic-filter-links-design.md

@@ -25,6 +25,7 @@ The acceptance criteria are:
 **In scope (this work):**
 
 - The core `filter_url()` helper.
+- The `OperatorFilter.where()` ergonomic constructor.
 - The date-range filtering capability the navbar links require.
 - Wiring the navbar "today" / "last 7 days" totals as links.
 
@@ -100,6 +101,81 @@ def filter_url(filter_obj: OperatorFilter, **extra_params: str) -> str:
   now.
 - `filter_presets.py` can adopt this helper later; not required for this change.
 
+### Component 1b — `OperatorFilter.where()` (ergonomic construction)
+
+Building filters via the explicit constructor is verbose, because each criterion
+must be wrapped and a `Modifier` imported:
+
+```python
+GameFilter(
+    purchase_count=IntCriterion(value=1, modifier=Modifier.GREATER_THAN),
+    playtime_hours=IntCriterion(modifier=Modifier.IS_NULL),
+)
+```
+
+Add a `where(**lookups)` classmethod on `OperatorFilter` (so every filter type
+inherits it) accepting Django-`QuerySet.filter()`-style `field__modifier=value`
+lookups:
+
+```python
+GameFilter.where(purchase_count__gt=1, playtime_hours__isnull=True)
+
+# combined with filter_url():
+filter_url(GameFilter.where(purchase_count__gt=1, playtime_hours__isnull=True))
+
+# the navbar filters become:
+filter_url(SessionFilter.where(timestamp_start=today_iso))
+filter_url(SessionFilter.where(timestamp_start__between=(week_ago_iso, today_iso)))
+```
+
+How it works (no new architecture — it builds the same dataclass instances):
+
+1. Split each kwarg into `(field_name, suffix)` on the last `__`.
+2. Resolve the field's criterion class from its dataclass annotation, reusing the
+   logic `from_json` already has (`common/criteria.py:439-473`). Factor that
+   resolution into a shared helper (e.g. `_criterion_class_for(cls, field)`) so
+   `from_json` and `where()` cannot drift — a small de-duplication bonus.
+3. Map the suffix to a `Modifier` (see table); no suffix → the criterion type's
+   natural default (`EQUALS` for scalar/string/bool, `INCLUDES` for the set
+   criteria `MultiCriterion` / `ChoiceCriterion`).
+4. Build the concrete criterion: scalar → `value`; a 2-tuple → `value` / `value2`
+   (for `between` / `not_between`); a list → the set criterion's `value`.
+5. Return a normal filter instance.
+
+Suffix → `Modifier` map:
+
+| suffix        | Modifier        |
+|---------------|-----------------|
+| *(none)*      | `EQUALS` (scalar/string/bool) / `INCLUDES` (set) |
+| `gt`          | `GREATER_THAN`  |
+| `lt`          | `LESS_THAN`     |
+| `ne`          | `NOT_EQUALS`    |
+| `between`     | `BETWEEN` (value is a 2-tuple) |
+| `not_between` | `NOT_BETWEEN` (value is a 2-tuple) |
+| `in`          | `INCLUDES` (set) |
+| `exclude`     | `EXCLUDES` (set) |
+| `all`         | `INCLUDES_ALL` (set) |
+| `contains`    | `INCLUDES` (string `icontains`) |
+| `regex`       | `MATCHES_REGEX` |
+| `isnull`      | `IS_NULL` (value ignored) |
+| `notnull`     | `NOT_NULL` (value ignored) |
+
+Design decisions:
+
+- **Purely additive.** The explicit constructor, `to_q()`, and serialization are
+  unchanged. `where()` is chosen over a custom `__init__` precisely to keep the
+  explicit `GameFilter(name=StringCriterion(...))` form **fully statically typed**
+  (a `@dataclass(init=False)` + `**kwargs` constructor would have erased that).
+- **Real field names, no aliasing.** Lookups use the actual dataclass field names
+  (e.g. `playtime_hours`, not a prettier `playtime`); no alias layer to maintain.
+- **Fail loud.** An unknown field name or an unknown/!type-incompatible suffix
+  raises a clear `ValueError`/`TypeError` rather than silently producing an empty
+  filter. The lookup form is dynamic (like Django's `.filter()`), so this runtime
+  validation replaces static checking for that form only.
+- **Scope.** `where()` covers the common flat-AND case (the verbose pain point).
+  `AND` / `OR` / `NOT` nesting continues to use the explicit constructor, which
+  reads fine and is rare.
+
 ### Component 2 — date-range filtering on session timestamps
 
 **Decision: switch `SessionFilter.timestamp_start` / `timestamp_end` to
@@ -144,8 +220,8 @@ The two navbar filters expressed with this:
 ### Component 3 — navbar wiring (and a consistency fix)
 
 - `model_counts` (`games/views/general.py`) computes `today_url` and
-  `last_7_url` with `filter_url(SessionFilter(...))` and adds them to its
+  `last_7_url` with `filter_url(SessionFilter.where(...))` (see Component 1b) and
-  returned dict alongside the existing formatted totals.
+  adds them to its returned dict alongside the existing formatted totals.
 - `NavbarPlaytime()` (`common/layout.py`) gains `today_url` / `last_7_url`
   parameters and wraps each total string in an `<a href>`. The out-of-band
   refresh call in `games/views/session.py:311` passes the new URLs too.
@@ -165,6 +241,14 @@ so only the 7-day computation changes.
   `filter` query param is the URL-encoded `filter_to_json(filter_obj)`; extra
   params are merged; the produced URL round-trips through `parse_session_filter`
   to an equivalent filter.
+- **`where()`** (unit): each suffix maps to the right `Modifier`; the resolved
+  criterion class matches the field annotation across criterion types
+  (`Int`/`String`/`Bool`/`Date`/`Multi`/`Choice`); `between` consumes a 2-tuple
+  into `value`/`value2`; no-suffix defaults to `EQUALS` for scalars and
+  `INCLUDES` for set criteria; `isnull`/`notnull` ignore the value;
+  `GameFilter.where(purchase_count__gt=1, playtime_hours__isnull=True)` produces a
+  filter equal to the explicit construction and yields the same `to_q()`; an
+  unknown field or suffix raises.
 - **Date filtering** (unit/db): sessions started today / 3 days ago / 10 days ago
   fall into the correct buckets for the "today" and "last 7 days" filters via
   `SessionFilter.to_q()`.