feat: Implement snapshot storage LRU and size limits

[joseph0926]

Problem

Default routeKey is location.pathname, causing snapshot explosion with dynamic routes like /items/1, /items/2, etc.

Proposed Solution

Add maxEntries option with LRU eviction
Provide route normalization guide (e.g., /items/:id pattern)
Consider optional compression (gzip/deflate or lighter alternatives)
Add snapshot size limit per entry

Affected Files

packages/prepaint/src/capture.ts
Related boot/snapshot storage logic