feat: day-progress gauge on Today's Pulse (multiple of a normal day)

[pitimon]

Summary

Adds a full-day-basis readout under Tokens & Cost — "today so far as a multiple of a normal full day" (e.g. 1.8×) — beside the existing same-elapsed deltas. Chosen after reviewing 4 candidate formulas against real data across the day (mockup):

• The deltas answer "heavier/lighter than usual, right now?" — steady all day (same-elapsed).
• The gauge answers "how much of a normal day have I burned?" — a fuel gauge that climbs through the day. It complements, not replaces.
• Rejected alternatives: naive full-day delta (flips sign in the morning), pace-projection (noisy early).

Changes

• computePulse: optional trailingFull (full-day 7-day average) → per-metric progress ratio for tokens/cost; null for $/MTok (a rate), non-day periods, or a zero baseline (guarded — no Inf).
• reduceDaySlices: also returns trailingFull = mean of the 7 trailing days summed to end-of-day. Reuses the already-fetched 7-day hourly data — no extra request. use-pulse spreads it straight through (no hook change).
• PulseCard: a 0–2× gauge with a "normal day" tick at 1×; a fill past the midpoint = today already outran a whole typical day. $/MTok keeps deltas only.

Test plan

• pulse-stats + pulse-plan unit tests (31, +4): progress ratio, $/MTok = null, no-baseline = null, zero-baseline guard, and trailingFull captures post-cutoff hours (differs from same-elapsed)
• Full dashboard vitest: 286 pass
• ci:local green — root 775, copy, ui-hardcode, guardrails 4/4
• Live (local serve, real data, 6 AM): gauge renders under Tokens (0.1×) & Cost (0.2×), fill width matches ratio on the 0–2× scale, $/MTok has no gauge
• Post-merge: fold into 0.39.33 release