feat: add prestige system and skill upgrades with comprehensive documentation

docs/task7/plan_page.md

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+# Refactor Plan: page.tsx
+
+## Current State
+- **File:** `src/app/page.tsx`
+- **Lines:** 650
+- **Target:** ≤400 lines (reduce by ~250 lines)
+
+## Proposed File Structure
+
+### 1. `src/components/game/tabs/PrestigeTab.tsx` (NEW, ≈60 lines)
+**Contains:**
+- `PrestigeTab` component (extracted from `renderGrimoireTab`)
+- Grimoire/Prestige tab UI
+
+**Rationale:** Self-contained tab component; only depends on store, PRESTIGE_DEF, GUARDIANS.
+
+### 2. `src/app/page.tsx` (≈300 lines)
+**Keeps:**
+- Main `ManaLoopGame` component shell
+- Tabs definition and lazy loading
+- Core game loop integration
+- Most tab content (other tabs remain via lazy loading)
+
+**Rationale:** Reduces main page by extracting only the Grimoire tab which is standalone.
+
+## Circular Import Risks
+
+**LOW RISK:**
+- `PrestigeTab` depends on store, PRESTIGE_DEF, GUARDIANS - all stable dependencies.
+- No circular dependency with `page.tsx`.
+
+**MITIGATION:**
+- Import store and constants normally in new component.
+
+## Extraction Order
+
+**1 → 2**
+
+1. Create `PrestigeTab.tsx`, move `renderGrimoireTab` content, adapt to be standalone (receive store via hook internally), export component.
+2. Update `page.tsx`: replace `renderGrimoireTab` call with `<PrestigeTab />`, remove extracted code.
+3. Verify typecheck, verify ≤400 lines.
+
+## Notes
+
+This addresses the main line bloat by only ~60 lines (renderGrimoireTab). To get page.tsx under 400 lines fully would require more extensive splitting (extracting each tab into separate route files, extracting sidebar, etc.). The plan here is conservative - if page.tsx is still >400 after extracting PrestigeTab, we can consider:
+- Extracting StatsTab/LabTab content further
+- Extracting activity log rendering
+- Extracting action buttons
+But per phase instructions we must get ALL THREE target files under 400 lines, so we must be more aggressive if needed.