Path to Freedom — capital pools, retirement model, depletion chart

[fleveque]

Summary

Builds on the v1 /freedom page (PR #179) with five follow-ups:

• Optional capital pools beyond dividend stocks: an interest-bearing pool (bonds / real estate / savings) and a growth pool (index funds / growth stocks). Reinvest-interest checkbox controls whether interest compounds during accumulation or counts toward the goal.
• Capped adaptive distribution: each post-goal year sells up to the inflation-adjusted shortfall, never more than 4% of capital-at-distribution (SWR-style ceiling, inflated yearly). Healthy retirements hit the goal exactly; lean ones get passive + 4% with the gap visible as acquisitive-power loss. Sales come from the growth pool first.
• Retirement-age trigger: optional motivation_retirement_age + motivation_birth_year. Forces distribution to start at that age even if the dividend goal hasn't been met — distribution proceeds with whatever passive income exists.
• Total-capital chart: dual-axis (capital left, monthly income right), continues past acquisitive-power loss until capital hits zero, with a rose-dashed vertical marker at the year real income is first lost. Two new insight stats: Real income lasts and Capital lasts.
• Bugfix: /freedom rendered blank on hard refresh because two useMemos sat below an early-return guard. Moved them above the guard so the hook count is stable between loading and loaded renders.

Other UX touches

• DEFAULT_MAX_YEARS 60 → 80 so realistic FIRE projections have room to deplete on the chart.
• X-axis tick selector switched from year-based to pixel-based collision detection (LABEL_MIN_PX) — anchors (today/goal/start/end) win over step ticks. Fixes overlapping +37y +38y and -2y 0 labels regardless of span.
• Optional motivation_birth_year renders an "age at this year" secondary row on the X axis of all three charts.
• Y-axis labels: trimDecimalZeros keeps $1.25M and $1.88M distinct (they both used to collapse to $1M).
• Reordered insight stat cards so the two post-goal numbers (Real income lasts, Capital lasts) sit in the top row instead of wrapping below.

Backend

• 5 migrations adding motivation_interest_capital, motivation_interest_rate_pct, motivation_growth_capital, motivation_growth_rate_pct, motivation_reinvest_interest, motivation_birth_year, motivation_retirement_age to users. (One short-lived motivation_birth_date was replaced by motivation_birth_year in the same series — followup migration, not a rollback.)
• MotivationProjectionService.simulate extended with all the new inputs; distribution_outcome implements the capped-adaptive rule. Cache invalidation triggers include every new field.
• ProfilesController permits + serializes the new fields; the demo bundle showcases all of them.
• TS twin in app/frontend/lib/motivation.ts stays in sync.

Test plan

• bundle exec rspec — full suite still green (716 examples).
• npx tsc --noEmit and npx vite build clean.
• bin/rubocop and bin/brakeman clean.
• Manual: visit /freedom, fill capital pools + retirement age, observe the three charts update + the new stat cards.
• Manual: hard-refresh /freedom (the bug from this PR) — page must render, not blank.
• Manual: set retirement age below the year the goal hits — distribution starts at retirement age, income line shows the SWR-capped shortfall, vertical "acquisitive power lost" bar lands at year 0 of distribution.
• Manual: visit /demo — same flows work from the prefilled demo profile.

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