proof(SafeColor): DISCHARGE WCAG-AA + WCAG-AAA threshold anchors via Refl (proven#90) (#105)

Ninth "overly cautious OWED" discharge of today's [proven#90 Phase
3](#90) campaign.

## What it does

\`\`\`idris
public export
wcagAAThreshold : (c1, c2 : RGB) -> meetsWCAG_AA c1 c2 = (contrastRatio
c1 c2 >= 4.5)
wcagAAThreshold _ _ = Refl

public export
wcagAAAThreshold : (c1, c2 : RGB) -> meetsWCAG_AAA c1 c2 =
(contrastRatio c1 c2 >= 7.0)
wcagAAAThreshold _ _ = Refl
\`\`\`

## Why it works

\`meetsWCAG_AA\` and \`meetsWCAG_AAA\` are \`public export\` with these
exact expressions as their bodies (SafeColor.idr L188-194). The LHS
unfolds directly to the RHS for \`Refl\` — no Double-comparison
reduction needed.

The OWED comments cited "Double-comparison opacity" — that blocker only
applies if you tried to REDUCE \`contrastRatio c1 c2 >= 4.5\` to a
concrete \`True\`/\`False\`. Here we don't reduce; we just state the
definitional equality between the wrapper and its body.

Refs #90

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

src/Proven/SafeColor/Proofs.idr

@@ -85,12 +85,20 @@ parseHexEmptyRejected = Refl
 -- OWED markers
 --------------------------------------------------------------------------------
 
-||| OWED: WCAG-AA threshold = 4.5. Blocked on Double-comparison opacity.
+||| DISCHARGED: WCAG-AA threshold = 4.5. `meetsWCAG_AA` is `public
+||| export` with body `contrastRatio c1 c2 >= 4.5` (SafeColor.idr
+||| L188-189), so the LHS unfolds directly to the RHS for `Refl`. No
+||| Double-comparison reduction is needed — both sides are literally
+||| the same expression.
 public export
-0 wcagAAThreshold :
+wcagAAThreshold :
   (c1, c2 : RGB) -> meetsWCAG_AA c1 c2 = (contrastRatio c1 c2 >= 4.5)
+wcagAAThreshold _ _ = Refl
 
-||| OWED: WCAG-AAA threshold = 7.0. Same blocker.
+||| DISCHARGED: WCAG-AAA threshold = 7.0. `meetsWCAG_AAA` is `public
+||| export` with body `contrastRatio c1 c2 >= 7.0` (SafeColor.idr
+||| L193-194) — same unfolding pattern as `wcagAAThreshold`.
 public export
-0 wcagAAAThreshold :
+wcagAAAThreshold :
   (c1, c2 : RGB) -> meetsWCAG_AAA c1 c2 = (contrastRatio c1 c2 >= 7.0)
+wcagAAAThreshold _ _ = Refl