W-451: Onboarding refresh + symbols on by default

[wr]

Reworks onboarding to feel less pushy and more useful.

What's in it

• New "Set up your features" step (Welcome → Set up your features → Permissions → Done): enable/disable Emoji, Symbols, GIF and pick each trigger, reusing the Settings section headers + trigger pickers.
• Removed the big "Replace system emoji picker" CTA step and the "More options" overlay. Replace is now a calm toggle on the Done screen; Automatic updates + Start at login sit in a second section there.
• Live "try it out" field on Done (autofocused, placeholder :smile) — DoneStep posts a mojitoShouldStartEngine notification so the engine starts early enough for shortcuts to expand right in the field.
• Stats consent moved into the onboarding Privacy details sheet (which marks consent seen on appear). Skipping it still fires the existing one-time consent prompt after onboarding, so nothing is sent before disclosure.
• Symbols now default ON for fresh installs (TriggerConfigStore.migrate + TriggerConfig.default), blended into emoji search via follow-emoji — matching emoji/GIF. Existing users' saved configs are untouched.

Test plan

• Onboarding: Welcome → Features (all three on; symbols "Same as emoji") → Permissions → Done.
• Done: replace toggle works; updates/login in their own section; the :smile field is focused and expands live.
• Skip Privacy details → consent prompt appears after finishing; open it → no prompt; nothing sent before either.
• Fresh config defaults symbols on; existing config unaffected.
• Unit suite green (228 tests; updated the symbols-default tests).

Notes

• Symbols-on-by-default is a behavior change for new installs — worth a v1.7.0 release note.

Independent code review: clean, no high-confidence issues.

Refs W-451

[linear-code]

W-451

[wr-claude-reviewer]

Reviewed the diff against CLAUDE.md conventions. This is a clean, well-scoped refactor:

• engine.start() → reconcile() → KeyMonitor.start() is idempotent (guards on !isRunning / !monitor.isRunning), so the new .mojitoShouldStartEngine notification handler in AppDelegate.swift safely overlaps with the existing start() calls in applicationDidFinishLaunching and the .mojitoOnboardingFinished handler — no double-tap risk.
• FeaturesStep mirrors GeneralSettings.swift's section headers / TriggerPicker wiring (including the takenOpens(excluding:) helper) field-for-field — confirmed by diffing the two.
• The symbols-default flip (TriggerConfig.default + TriggerConfigStore.migrate's fallback ?? true) only changes behavior for configs with no persisted PrefsKey.triggers blob (fresh installs, per the PR description) — existing installs already have that blob from the prior migration and hit the early-return decode path in load(), untouched. Tests were updated consistently (migrationOnEmptyDefaultsEnablesAllFeatures, symbolsTriggerDefaultsOn).
• Telemetry consent: moving the toggle into PrivacyDetailsSheet and stamping telemetryConsentSeen there, with the existing TelemetryConsent.presentIfNeeded() fallback after onboarding finishes, preserves the "nothing sent before disclosure" invariant either way (sheet opened or skipped).
• No leftover references to the removed ReplaceEmojiStep.

CI (ssot workflow) was still in progress at review time with no failures reported, so not treating it as blocking.

Nit: FeaturesStep (OnboardingScreens.swift) duplicates GeneralSettings.swift's takenOpens(excluding:) helper and the three Section/SettingsSectionHeader/TriggerPicker blocks verbatim. Not required to fix, but if this pattern gets a third caller, worth factoring into a shared view.