Phase A1: jargon-free flavor on all reachable spell Descriptions

The audit plan flagged jargon leaks in the SRD spell prose surfaced by
!cast and !spellbook. Verifying against HEAD turned up two corrections
to the plan's framing:

- The overlay in dnd_spells_data.go wins on ID collision, so for the
  ~76 hand-authored spells the *overlay* Descriptions are what players
  actually see — and those were crunchier than the SRD ("Heal 1d8 +
  WIS mod HP. Touch.", "8d6 fire in 20 ft radius. DEX save half.",
  etc.). Touching only the generated SRD file would have missed the
  bigger leak.
- The Upcast field is never displayed at runtime (only the import
  generator reads it), so testing it against the regex would test
  dead data.

So this commit:
- rewrites every overlay Description into playful, jargon-free flavor
  in the charm_person voice ("Sweet-talk a humanoid…") — no dice, no
  saves, no AC math, no ability-mod references
- adds 31 overlay shims for SRD-only spells whose generated text was
  broken (placeholder gaps from the Open5e classifier — "no larger
  than a.", "up to to", "in a in range"), empty ("You touch a
  creature."), typo-laden ("magicou", "undeadou", "diseasesou"), or
  jargon-heavy (false_life's "1d4+4 temporary hit points")
- adds TestSpellDescriptionsAreJargonFree, a regex sweep over the
  merged registry that bans "saving throw", "spell slot of",
  "ability modifier", "hit points equal to", and \bNdN\b dice
  notation. Currently passing; will fail-loud on regressions or new
  SRD imports that need overlay shims.

The generated dnd_spells_srd_data.go is left untouched — overlay is
the regen-safe surface per its own header comment.

internal/plugin/dnd_spells_prose_test.go

@@ -0,0 +1,45 @@
+package plugin
+
+import (
+	"regexp"
+	"testing"
+)
+
+// TestSpellDescriptionsAreJargonFree scans every reachable spell Description
+// in the merged registry (SRD + hand-authored overlay) for D&D jargon that
+// leaks into player-facing chat via dnd_cast.go's !cast confirmation and the
+// !spellbook list view. Per feedback_accessibility_over_dnd_crunch, the
+// player surface should be verb/outcome-led — no math, no dice, no saves.
+//
+// Failures usually mean either (a) a new SRD entry was added without an
+// overlay shim in dnd_spells_data.go, or (b) an overlay Description was
+// edited back into crunch. Fix in dnd_spells_data.go; do NOT touch the
+// generated dnd_spells_srd_data.go directly (it's regenerated from Open5e).
+//
+// Upcast strings are NOT tested — they're never displayed (grep
+// `\.Upcast` across the codebase to confirm; only the import generator
+// reads them as of 2026-05-15).
+func TestSpellDescriptionsAreJargonFree(t *testing.T) {
+	bans := []struct {
+		name string
+		re   *regexp.Regexp
+	}{
+		{"saving throw", regexp.MustCompile(`(?i)saving throw`)},
+		{"spell slot of", regexp.MustCompile(`(?i)spell slot of`)},
+		{"ability modifier", regexp.MustCompile(`(?i)ability modifier`)},
+		{"hit points equal to", regexp.MustCompile(`(?i)hit points equal to`)},
+		{"NdN dice notation", regexp.MustCompile(`\b\d+d\d+\b`)},
+	}
+
+	for id, s := range dndSpellRegistry {
+		if s.Description == "" {
+			continue
+		}
+		for _, b := range bans {
+			if b.re.MatchString(s.Description) {
+				t.Errorf("spell %q Description leaks %q jargon: %q",
+					id, b.name, s.Description)
+			}
+		}
+	}
+}