Align set-criterion modifiers with Stash (any/all/none) and harmonize EXCLUDES

Closes #10.

Backend (common/criteria.py):
- Treat `excludes` as an always-orthogonal AND'd negative across both
  MultiCriterion and ChoiceCriterion; the modifier now governs only the
  `value` (include) set. This removes the prior divergence where
  MultiCriterion.EXCLUDES dropped the excludes list and ChoiceCriterion.EXCLUDES
  swapped include/exclude into a positive.
- Fold INCLUDES / INCLUDES_ALL / EXCLUDES (+ EQUALS/NOT_EQUALS aliases) into the
  shared _SetCriterion base so the two subclasses cannot drift; remove _extra_q.

M2M "has all" (games/filters.py):
- PurchaseFilter._games_to_q builds a pk__in subquery with one join per value so
  INCLUDES_ALL on the many-to-many games field works in a single .filter()
  (a naive Q(games=a) & Q(games=b) collapses to one join and matches nothing).

UI (FilterSelect + filter_bar.js):
- Add an optional any/all/none match-mode <select> (INCLUDES/INCLUDES_ALL/
  EXCLUDES) rendered before the pills via a new `leading` slot on the shared
  combobox shell. A native control so its value is its state. readSearchSelect
  serialises it to data-match; filter_bar folds it into the criterion modifier.
  Orthogonal to the (Any)/(None) presence pseudo-options and the exclude channel.
- Enable it for the M2M Purchase.games field (INCLUDES_ALL is only meaningful
  for multi-valued relations). Styled with already-compiled utilities.

Tests: harmonized EXCLUDES + INCLUDES_ALL for both criterion types, a DB-backed
INCLUDES_ALL vs INCLUDES contrast on Purchase.games, and FilterSelect /
PurchaseFilterBar rendering + round-trip of the match mode.

https://claude.ai/code/session_01KwVrGFbq13mZdhDL9G6zhg

games/static/js/filter_bar.js

@@ -67,16 +67,21 @@
       var field = widget.getAttribute("data-name");
       var included = parseJSONAttr(widget, "data-included");
       var excluded = parseJSONAttr(widget, "data-excluded");
-      var modifier = widget.getAttribute("data-modifier");
-      if (modifier === "NOT_NULL" || modifier === "IS_NULL") {
-        filter[field] = { modifier: modifier };
+      // Two orthogonal axes: a presence modifier (NOT_NULL/IS_NULL) from the
+      // pinned (Any)/(None) pseudo-options clears the value set, while the
+      // match mode (INCLUDES/INCLUDES_ALL/EXCLUDES) governs how the include set
+      // matches. Fields without a match-mode select default to INCLUDES.
+      var presence = widget.getAttribute("data-modifier");
+      var match = widget.getAttribute("data-match") || "INCLUDES";
+      if (presence === "NOT_NULL" || presence === "IS_NULL") {
+        filter[field] = { modifier: presence };
       } else if (included.length > 0 || excluded.length > 0) {
         // All filter pills carry {id, label}; store them as-is so the filter
         // URL and saved presets are self-describing (Stash-style).
         filter[field] = {
           value: included.map(function (item) { return {id: item.id, label: item.label}; }),
           excludes: excluded.map(function (item) { return {id: item.id, label: item.label}; }),
-          modifier: modifier || "INCLUDES",
+          modifier: match,
         };
       }
     });

games/static/js/search_select.js

@@ -447,6 +447,11 @@
         container.setAttribute("data-excluded", JSON.stringify(excluded));
         if (modifier) container.setAttribute("data-modifier", modifier);
         else container.removeAttribute("data-modifier");
+        // The match-mode <select> (any/all/none) governs how the include set
+        // matches; its value is the criterion modifier. A native control, so its
+        // value is read directly — no pill bookkeeping.
+        var matchSelect = container.querySelector("[data-search-select-match]");
+        if (matchSelect) container.setAttribute("data-match", matchSelect.value);
         return;
       }
       var values = pills