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>

scripts/__tests__/atom-discovery.test.ts

@@ -10,7 +10,7 @@ async function load(): Promise<DiscoveredAtom[]> {
   return atoms
 }
 
-describe('discoverAtoms — reference children', () => {
+describe('discoverAtoms: reference children', () => {
   it('emits top-level skills with parent_atom_id null', async () => {
     const all = await load()
     const vat = all.find((a) => a.id === 'horizontal/swedish-vat')

scripts/__tests__/generate-skill-bodies.test.ts

@@ -22,7 +22,7 @@ function atom(overrides: Partial<DiscoveredAtom>): DiscoveredAtom {
 }
 
 describe('buildMigrationSql', () => {
-  it('dollar-quotes bodies with backticks, $$, quotes, and the default tag — round-trips intact', () => {
+  it('dollar-quotes bodies with backticks, $$, quotes, and the default tag: round-trips intact', () => {
     const tricky = 'Body with `code`, $$dollars$$, \'single\' and "double" quotes, and a $gb$ tag.'
     const sql = buildMigrationSql([atom({ body: tricky, description: tricky })], { 'horizontal/test': 1 })
 
@@ -49,7 +49,7 @@ describe('buildMigrationSql', () => {
     expect(sql).toContain("'O''Brien & Co'")
   })
 
-  it('emits parent_atom_id — NULL for top-level skills, a quoted id for reference children', () => {
+  it('emits parent_atom_id: NULL for top-level skills, a quoted id for reference children', () => {
     const sql = buildMigrationSql(
       [
         atom({ id: 'horizontal/swedish-vat', parent_atom_id: null }),