GymLog: tier PR border by overall / phase / rep

[nt1998]

Summary

Splits the in-workout PR highlight into three colour-coded tiers without changing layout. The PR-info bar and the highlighted work-set row now read at a glance:

• 🔴 Red — new all-time weight PR (overall)
• 🟡 Yellow — new top weight within the current phase, but not all-time
• 🟢 Green — same weight as the prior best, more reps (rep PR)

The previous code only had a 2-state distinction (weight PR / rep PR), both compared against the all-time best.

Changes

• src/tabs/GymLog.jsx — getExercisePR now returns { overall, phase } buckets, walked once over committed workouts prior to the current date. Phase scope is the open phase (!p.end); falls back to all-time when no phase is open. Derives a single prTier ('overall' | 'phase' | 'rep' | null) from today's best work set vs both buckets.
• src/App.jsx — passes phases into <GymLog>.
• src/App.css — adds --acc-red-bg + --acc-green-bg-grad, renames the PR classes (new-overall-pr / new-phase-pr / new-rep-pr and set-row.overall-pr / .phase-pr / .rep-pr), and maps each to its accent colour. Existing layout / sizes untouched.

Test plan

• In a current phase, log a set that beats the all-time top weight → PR bar + set row turn red
• Log a set that beats the current phase top but not all-time → yellow
• Log a set matching the prior top weight but with more reps → green
• No PR → bar stays neutral, shows prior PR value
• Switch to light theme and verify all three colour combos remain legible

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