refactor(m4): full-bleed matrix + word-only line breaks

Two follow-up tweaks per user feedback ("wrap sur les mots, agrandit le
cadre"):

- Full-bleed wrapper: the matrix breaks out of the page's max-w-page (1400px)
  constraint via `margin: 0 calc(50% - 50vw)` + `width: 100vw`, mirroring the
  60px page padding internally. On wide viewports the picker now uses the
  ENTIRE viewport width, so column widths grow proportionally — names that
  used to wrap on 3 lines now fit on 1-2.
- Word-only wrapping: replaced `break-words` (overflow-wrap: break-word,
  which falls back to mid-word breaks) with `break-normal hyphens-none`
  (overflow-wrap: normal + word-break: normal). Cells break only at word
  boundaries; if a single word is longer than the cell it overflows
  visually rather than splitting `Aut\nhentication`-style. The grid is
  configured `minmax(7rem, 1fr)` so the minimum column is wide enough for
  every single word in MITRE v19 names, and stretches with available space.
- Spec §F2 rewritten as a bullet contract locking in: full-bleed, 15 cols
  minmax(7rem, 1fr), word-only wrap, font sans 12px / count 10px, headers/
  cells show name-only with external_id on hover + chips. Future spec-reviewer
  passes can grade against this.

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

frontend/src/components/MitreTagPicker.tsx

@@ -130,10 +130,13 @@ export function MitreTagPicker({ value, onChange, className }: MitreTagPickerPro
           data-testid="mitre-matrix-scroll"
           role="region"
           aria-label="MITRE ATT&CK matrix"
-          /* Equal-width columns share the container; no horizontal scroll. */
-          className="grid gap-px bg-border rounded"
+          /* `minmax(7rem, 1fr)` ensures every cell is wide enough for the
+           * longest single word in MITRE names (no mid-word breaks), and
+           * stretches to fill the container otherwise. Horizontal scroll only
+           * kicks in on narrow viewports below ~1680px. */
+          className="grid gap-px bg-border rounded overflow-x-auto"
           style={{
-            gridTemplateColumns: `repeat(${matrix.data.tactics.length}, minmax(0, 1fr))`,
+            gridTemplateColumns: `repeat(${matrix.data.tactics.length}, minmax(7rem, 1fr))`,
           }}
         >
           {matrix.data.tactics.map((tactic) => {
@@ -166,7 +169,7 @@ export function MitreTagPicker({ value, onChange, className }: MitreTagPickerPro
                   data-testid={`mitre-tactic-${tactic.external_id}`}
                   aria-pressed={tacticSel}
                 >
-                  <div className="text-xs font-semibold leading-tight break-words">
+                  <div className="text-xs font-semibold leading-tight break-normal hyphens-none">
                     {tactic.name}
                   </div>
                   <div className="text-[10px] text-text-dim mt-0.5">
@@ -205,7 +208,7 @@ export function MitreTagPicker({ value, onChange, className }: MitreTagPickerPro
                                 name: tech.name,
                               })
                             }
-                            className="flex-1 min-w-0 text-left px-2 py-1.5 font-sans break-words"
+                            className="flex-1 min-w-0 text-left px-2 py-1.5 font-sans break-normal hyphens-none"
                             title={`${tech.external_id} — ${tech.name}`}
                             data-testid={`mitre-technique-${tech.external_id}`}
                             aria-pressed={techSel}
@@ -250,7 +253,7 @@ export function MitreTagPicker({ value, onChange, className }: MitreTagPickerPro
                                     })
                                   }
                                   className={cn(
-                                    'block w-full text-left pl-5 pr-2 py-1 font-sans text-xs border-l-2 break-words',
+                                    'block w-full text-left pl-5 pr-2 py-1 font-sans text-xs border-l-2 break-normal hyphens-none',
                                     subSel
                                       ? 'accent-fill-purple border-purple text-text-bright'
                                       : 'border-purple/30 hover:bg-purple/10',

frontend/src/pages/MitrePage.tsx

@@ -92,7 +92,21 @@ export function MitrePage() {
       </div>
 
       <SectionHeader prefix="Tag" highlight="Picker" accent="orange" />
-      <MitreTagPicker value={selected} onChange={setSelected} />
+      {/* Full-bleed the matrix beyond max-w-page so it uses the full viewport
+       * width. `calc(50% - 50vw)` is the canonical CSS recipe: the element's
+       * left edge slides back to viewport x=0 regardless of how big the
+       * outer max-w-page container is. `px-[60px]` mirrors the page padding
+       * so cells don't touch the viewport edge. */}
+      <div
+        className="px-[60px]"
+        style={{
+          marginLeft: 'calc(50% - 50vw)',
+          marginRight: 'calc(50% - 50vw)',
+          width: '100vw',
+        }}
+      >
+        <MitreTagPicker value={selected} onChange={setSelected} />
+      </div>
 
       {selected.length > 0 && (
         <Card accent="purple" className="mt-6" title="Selected (preview payload)">