Rename SpeakUp to Pladder

[dinooo13]

Why

The name SpeakUp collided with getspeakup.app (similar name and logo). The new name is Pladder — Low German (Plattdeutsch) for to babble: you pladder into the microphone, and clean text comes out. After a full collision sweep (apps, domains, trademarks, GitHub) the name is unclaimed.

What changed

• Package, products, targets and directories: SpeakUp* → Pladder* (PladderCore, PladderAudio, PladderSystem, PladderEngines, PladderBench, PladderCLI)
• CLI: speakup-cli → pladder-cli
• Bundle ID: de.speakup.app → de.dinooo13.pladder
  • Consequence: macOS keys Accessibility/Microphone grants to the bundle signature, so permissions must be re-granted once after installing the renamed build.
• One-time settings migration: on first launch the app copies ~/Library/Application Support/SpeakUp/settings.json to Pladder/settings.json if the new file does not exist; the old file stays in place.
• README: renames plus a new The name section explaining pladdern
• Docs updated throughout: CLAUDE.md, INSTALL.md, docs/BENCHMARKS.md, issue template, CI artifact names

Not changed

• Anything on the release-to-paste path (pure naming/identity) — no benchmark re-run required per CLAUDE.md. Build, tests and bundling verified locally.
• Repo URLs in docs already point at dinooo13/pladder; the GitHub repo rename itself happens after this PR merges (it breaks clone URLs and the badge, so it goes last).

Verification

• swift build ✅
• swift test ✅ 59 tests
• CODESIGN_IDENTITY=- ./scripts/bundle.sh ✅ → dist/Pladder.app