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>

app/api/import/articles/execute/route.ts

@@ -28,7 +28,7 @@ function nameKey(value: string | null): string | null {
  * POST /api/import/articles/execute
  *
  * Imports validated article rows. Duplicates (matched by article number, then
- * by name) are either updated (merge — only non-empty fields overwrite) or
+ * by name) are either updated (merge: only non-empty fields overwrite) or
  * skipped based on `update_duplicates`. An optional BAS revenue-account override
  * is kept only when it is an active class-3 account; unknown/inactive accounts
  * are dropped (with a warning) rather than mutating the chart of accounts.
@@ -86,8 +86,8 @@ export const POST = withRouteContext(
           droppedAccounts.add(acc)
           warnings.push(
             status === 'activatable'
-              ? `Försäljningskonto ${acc} är inte aktiverat i kontoplanen — artiklar importerades utan kontoöverstyrning.`
-              : `Försäljningskonto ${acc} är ogiltigt — ignorerades.`,
+              ? `Försäljningskonto ${acc} är inte aktiverat i kontoplanen. Artiklar importerades utan kontoöverstyrning.`
+              : `Försäljningskonto ${acc} är ogiltigt, ignorerades.`,
           )
         }
         return null
@@ -147,7 +147,7 @@ export const POST = withRouteContext(
           continue
         }
 
-        // No match — create.
+        // No match, create.
         const { data, error } = await supabase
           .from('articles')
           .insert({
@@ -170,7 +170,7 @@ export const POST = withRouteContext(
           .single()
 
         if (error) {
-          // Unique violation on (company_id, article_number) — treat as a soft
+          // Unique violation on (company_id, article_number): treat as a soft
           // skip (manual number collided with an existing or in-batch article).
           if (error.code === '23505') {
             skipped++