chore: remove dead Danish translation keys

[detail-app]

Issue for this PR

Closes #32

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Removes 48 unused Danish (da.ts) translation overrides that have zero production consumers anywhere in the codebase. Each key was confirmed via ripgrep to appear only inside the i18n/.ts files. The keys were orphaned by earlier commits that removed their callers (e.g. the Go page testimonials section, the Go privacy section, the workspace keys "Last Used" column, the referral rewards subtitle/empty fallbacks, and the referral source/status/apply button keys replaced by the new description. / action.* scheme).

Keys removed:

• nav.changelog, nav.discord, nav.x (born dead; footer.* siblings used)
• go.cta.start (replaced by go.cta.template/text/price/promo)
• go.graph.free, go.graph.freePill, go.graph.aria (free-usage bar removed)
• go.testimonials.* (21 keys; testimonials section removed from /go)
• go.privacy.* (5 keys; privacy section removed from /go)
• go.faq.a5.beforeExceptions, go.faq.a5.exceptionsLink (replaced by go.faq.a5.body)
• workspace.keys.table.lastUsed (Last Used column removed)
• workspace.referral.rewards.subtitle, rewards.empty (replaced by title/description)
• workspace.referral.reward.source.{pendingInvitee,available,applied}, reward.status.{applied,pendingInviter,pendingInvitee}, apply.{noGo,preview,action} (replaced by description.* / action.* scheme)
• download.hero.subtitle (download hero restructured)

How did you verify your code works?

Each removed key was verified via ripgrep to have no callers outside the i18n/*.ts files themselves.

Screenshots / recordings

N/A — no UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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