docs(achievements): v1.4.18 expansion research with 20+ proposed achievements

Benchmark Apple Health, Withings, Oura, Strava, Habitica. Pick a
mood category, an entry-consistency category, and a small hidden /
Easter-egg group. Lock in the discovery rule (only show public
achievements when the user has data for the metric).

Total proposed: 15 public + 6 hidden = 21, taking the roster from
38 to 59.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.planning/v1418-achievements-research.md

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+# v1.4.18 — achievements expansion research
+
+## Benchmarking
+
+We surveyed five reference systems before sketching the new HealthLog
+achievement set:
+
+- **Apple Health (Activity rings, Workouts)** — month-of-perfect-days,
+  ring-on-fire weeks, doubled-goal challenges. Tone is *celebratory but
+  optional*; nothing shames you for missing a ring.
+- **Withings (Health+)** — milestone-based ("First weigh-in", "100
+  weigh-ins"), trend-based ("Lost 1 kg", "Maintained ±2 kg for 30 d"),
+  and seasonal challenges. Notable: never fires a coercive "you missed
+  a day" badge.
+- **Oura** — readiness streaks, sleep regularity, recovery PRs, "first
+  workout of the year". Heavy use of personal-baseline comparisons (no
+  social leaderboard).
+- **Strava** — local-legend / monthly-goal / segment-hunting; explicit
+  social comparison. Not a fit for HealthLog (no sharing surface).
+- **Habitica** — gamified to-do; daily streaks with grace days, tag-
+  based achievements, hidden lore unlocks. The "hidden quest" pattern
+  is the inspiration for our Easter eggs.
+
+## Categories that fit HealthLog
+
+Keep the existing four (medication / vitals / security / engagement)
+and introduce two new buckets: **mood** and **hidden** (the Easter-egg
+group). Add two cross-cutting *axes* that aren't categories per se:
+discovery (only earnable when the user has data for the metric) and
+celebration (a special toast when a hidden one fires).
+
+Categories explicitly **avoided** (per Marc's brief):
+
+- Coercive volume nudges ("you measured the most this week!") — bad
+  incentive for a self-tracked health PWA.
+- Diagnostic framing ("hypertensive milestone") — never reward a
+  classification that is medical bad news.
+- Social-comparison ranking — there is no social surface to support it.
+
+## Discovery rule
+
+A public achievement (non-hidden) is only **shown to the user** when
+the precondition predicate is satisfied. Predicate examples:
+
+- mood badges → user has at least one `MoodEntry`
+- weight badges → user has at least one `Measurement` of type `WEIGHT`
+- BP/pulse badges → user has at least one `BLOOD_PRESSURE_SYS` /
+  `PULSE` measurement
+- medication badges → user has at least one active `Medication`
+
+Hidden Easter-eggs are *always shown as opaque "?" cards* but never
+leak their conditions in the DOM, so a curious user knows the slot
+exists without learning the trigger.
+
+## Public proposals (15)
+
+1. `mood-first` — "First mood entry" (1 pt, mood, milestone) — log any
+   mood. Precondition: user can earn once they have any data path open.
+2. `mood-streak-7` — "Mood diarist" (45 pt) — 7 consecutive days of
+   mood logged.
+3. `mood-streak-30` — "Mood diarist · 30 d" (180 pt).
+4. `mood-up-7` — "Brighter week" (90 pt) — 7-day mood mean improved by
+   ≥ 1.0 vs. previous 7-day window. Personal baseline only.
+5. `weight-first` — "First weigh-in" (8 pt, vitals).
+6. `weight-50` — "Fifty weigh-ins" (90 pt).
+7. `weight-200` — "Two hundred weigh-ins" (320 pt).
+8. `bp-first` — "First reading" (8 pt) — first BP measurement.
+9. `bp-50` — "Fifty BP readings" (90 pt).
+10. `bp-200` — "Two hundred BP readings" (320 pt).
+11. `pulse-first` — "First pulse log" (8 pt).
+12. `month-25-entries` — "Consistent month" (140 pt) — at least 25
+    distinct days with any entry inside one calendar month (Berlin TZ).
+13. `entry-streak-7` — "Tracker streak 7 d" (70 pt) — 7 consecutive
+    days with at least one measurement OR mood OR intake.
+14. `entry-streak-30` — "Tracker streak 30 d" (260 pt).
+15. `weekend-warrior` — "Weekend tracker" (40 pt) — logged data on 4
+    consecutive Sat+Sun pairs.
+
+## Hidden Easter-eggs (6)
+
+- `hidden-night-owl` — logged any entry between 02:00–04:00 Berlin
+  local. Single occurrence. Title only revealed on unlock.
+- `hidden-early-bird` — logged any entry between 04:00–06:00 Berlin.
+- `hidden-leap-day` — logged any entry on Feb 29.
+- `hidden-doctor-pdf` — exported a doctor-report PDF for the first
+  time (uses an existing audit log row for the trigger).
+- `hidden-locale-flip` — switched UI locale at least once
+  (audit log: `settings.locale.update`).
+- `hidden-bug-buddy` — submitted ≥ 5 bug reports (extending the
+  existing single bugReport milestone with a playful follow-on).
+
+Total new achievements: 15 public + 6 hidden = **21**, taking the
+roster from 38 → 59. Co-Authored by Claude Opus 4.7.