style: remove em/en dashes repo-wide, add CLAUDE.md rule against them (#890)

Em dashes (—) and en dashes (–) had spread across comments, docs, tests,
and a few UI strings, reading as AI-generated boilerplate rather than
house style. Replaced each with punctuation matching its context: colon
for explanatory clauses, comma for asides, plain hyphen for numeric/legal
ranges (e.g. "21-23§"), "to"/"till" for date ranges, parentheses for
paired-dash asides. messages/en.json and messages/sv.json were fixed by
hand together to keep sv/en in sync.

Left untouched where the dash is the functional subject rather than
decorative punctuation: date-range-parser.ts's separator regex,
charset-repair.ts's CP1252 byte-mapping table (and its test), the SIE
encoding mojibake docs, generic-csv.ts's minus-sign normalizer, the
agent system-prompt files that already instruct against em dashes, and
a golden iXBRL test fixture compared byte-for-byte.

Also fixes two bugs surfaced along the way: an off-by-one in
ApiKeysPanel's scope-label split (a leftover from an earlier partial
pass), and a charset-repair test that had lost the literal en-dash it
exists to verify.

Regenerated the agent atom seed migration (skills:generate) since 27
SKILL.md files changed. Added a CLAUDE.md rule against em/en dashes,
with an explicit carve-out for the functional-dash cases above.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

components/extensions/shared/MockDataImportDialog.tsx

@@ -303,7 +303,7 @@ export default function MockDataImportDialog<T>({
           <div className="space-y-4">
             <div className="flex items-center gap-2 text-sm text-muted-foreground">
               <FileSpreadsheet className="h-4 w-4" />
-              <span>{fileName} — {csvRows.length} rader</span>
+              <span>{fileName}: {csvRows.length} rader</span>
             </div>
 
             <div className="space-y-3">
@@ -323,7 +323,7 @@ export default function MockDataImportDialog<T>({
                       <SelectValue placeholder="Välj kolumn..." />
                     </SelectTrigger>
                     <SelectContent>
-                      <SelectItem value="___none___">— Välj kolumn —</SelectItem>
+                      <SelectItem value="___none___">- Välj kolumn -</SelectItem>
                       {csvHeaders.map(h => (
                         <SelectItem key={h} value={h}>{h}</SelectItem>
                       ))}
@@ -379,7 +379,7 @@ export default function MockDataImportDialog<T>({
 
             <div className="flex items-center gap-2 p-3 rounded-md bg-success/10 text-success text-sm">
               <Check className="h-4 w-4 shrink-0" />
-              <span>Giltig JSON — {jsonSummary}</span>
+              <span>Giltig JSON: {jsonSummary}</span>
             </div>
 
             <DialogFooter>