Implement GET /api/today endpoint (P1.4)

Add the core daily snapshot API that powers the dashboard. Returns:
- Training decision (status, reason, icon) using decision engine
- Cycle data (cycleDay, phase, phaseConfig, daysUntilNextPhase)
- Biometrics (hrvStatus, bodyBattery, weekIntensity, phaseLimit)
- Nutrition guidance (seeds, carbRange, ketoGuidance)

When no DailyLog exists (Garmin not synced), returns sensible defaults:
hrvStatus="Unknown", bodyBattery=100, weekIntensity=0. This allows
the app to function without Garmin integration.

22 tests covering auth, validation, all decision paths, override
handling, phase-specific logic, and nutrition guidance.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

IMPLEMENTATION_PLAN.md

@@ -29,7 +29,7 @@ This file is maintained by Ralph. Run `./ralph-sandbox.sh plan 3` to generate ta
 | PATCH /api/user | 501 | Returns Not Implemented |
 | POST /api/cycle/period | **COMPLETE** | Logs period start, updates user, creates PeriodLog (8 tests) |
 | GET /api/cycle/current | **COMPLETE** | Returns cycle day, phase, config, daysUntilNextPhase (10 tests) |
-| GET /api/today | 501 | Returns Not Implemented |
+| GET /api/today | **COMPLETE** | Returns decision, cycle, biometrics, nutrition (22 tests) |
 | POST /api/overrides | 501 | Returns Not Implemented |
 | DELETE /api/overrides | 501 | Returns Not Implemented |
 | POST /api/garmin/tokens | 501 | Returns Not Implemented |
@@ -73,6 +73,7 @@ This file is maintained by Ralph. Run `./ralph-sandbox.sh plan 3` to generate ta
 | `src/app/api/user/route.test.ts` | **EXISTS** - 4 tests (GET profile, auth, sensitive field exclusion) |
 | `src/app/api/cycle/period/route.test.ts` | **EXISTS** - 8 tests (POST period, auth, validation, date checks) |
 | `src/app/api/cycle/current/route.test.ts` | **EXISTS** - 10 tests (GET current cycle, auth, all phases, rollover, custom lengths) |
+| `src/app/api/today/route.test.ts` | **EXISTS** - 22 tests (daily snapshot, auth, decision, overrides, phases, nutrition, biometrics) |
 | `src/lib/nutrition.test.ts` | **MISSING** |
 | `src/lib/email.test.ts` | **MISSING** |
 | `src/lib/ics.test.ts` | **MISSING** |
@@ -176,12 +177,17 @@ Minimum viable product - app can be used for daily decisions.
 - **Why:** Dashboard needs this for display
 - **Depends On:** P0.1, P0.2, P1.2
 
-### P1.4: GET /api/today Implementation
-- [ ] Return complete daily snapshot with decision, biometrics, nutrition
+### P1.4: GET /api/today Implementation ✅ COMPLETE
+- [x] Return complete daily snapshot with decision, biometrics, nutrition
 - **Files:**
-  - `src/app/api/today/route.ts` - Implement GET aggregating all data sources
+  - `src/app/api/today/route.ts` - Implemented GET with `withAuth()` wrapper, aggregates cycle, biometrics, and nutrition
 - **Tests:**
-  - `src/app/api/today/route.test.ts` - Test decision computation, data assembly
+  - `src/app/api/today/route.test.ts` - 22 tests covering auth, validation, decision calculation, overrides, phases, nutrition
+- **Response Shape:**
+  - `decision` (status, reason, icon), `cycleDay`, `phase`, `phaseConfig`, `daysUntilNextPhase`, `cycleLength`
+  - `biometrics` (hrvStatus, bodyBatteryCurrent, bodyBatteryYesterdayLow, weekIntensityMinutes, phaseLimit)
+  - `nutrition` (seeds, carbRange, ketoGuidance)
+- **Fallback Behavior:** When no DailyLog exists (Garmin not synced), returns defaults: hrvStatus="Unknown", BB=100, weekIntensity=0
 - **Why:** This is THE core API for the dashboard
 - **Depends On:** P0.1, P0.2, P0.3, P1.3
 
@@ -487,6 +493,7 @@ P2.14 Mini calendar
 - [x] **GET /api/user** - Returns authenticated user profile, 4 tests (P0.4)
 - [x] **POST /api/cycle/period** - Logs period start date, updates user, creates PeriodLog, 8 tests (P1.2)
 - [x] **GET /api/cycle/current** - Returns cycle day, phase, phaseConfig, daysUntilNextPhase, cycleLength, 10 tests (P1.3)
+- [x] **GET /api/today** - Returns complete daily snapshot with decision, biometrics, nutrition, 22 tests (P1.4)
 
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