fix(lib): bound the memory cache, follow fetch redirect rules, lint chained test modifiers - #2447

🟢 Confidence 10/10 · safe to merge. Eviction, redirect and lint fixes are pinned by new tests; only the deliberate one-character truncate duplication (F1) is left open.
_{1 note · tests covered · risk medium}

Bounds the in-memory cache backend, makes non-strict redirects follow the fetch standard, and stops test-slop skipping chained test modifiers, plus a shared-helper cleanup across email, status-page and chat-platform. Safe to merge; only the deliberate one-character truncate duplication (F1) stays open.

• makeMemoryBackend sweeps expired entries on put once the map doubles past 256
• Non-strict redirects now turn 301/302 POST and 303 non-GET into a body-less GET
• escapeHtml and truncate move to @maple/strings; email keeps its own truncate
• test-slop walks chained modifiers such as it.effect.each(rows)

Still open from earlier reviews

• 🔵 Note · F1 · Two truncate helpers now cut one character apart · lib/strings/src/index.ts:82

Production impact

_{b394a3d · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}