Replace narrow lodash usage with native equivalents

[drernie]

Sub-task of #4869.

Why

21 import sites, all using cherry-picked subpaths (`lodash/foo`). Most are trivially replaceable with native ES or one-liners — eliminates one supply-chain dependency.

Inventory

```
identity, isFunction, isEmpty, isEqual, isString, isNil,
isArrayBuffer, isBuffer, isTypedArray,
mapValues, defaultTo, deburr, sampleSize,
memoize, template
```

Native / trivial replacements:

• `identity`, `isFunction`, `isEmpty`, `isEqual` (shallow), `isString`, `isNil` → one-liners
• `isArrayBuffer`, `isBuffer`, `isTypedArray` → `instanceof ArrayBuffer`, `Buffer.isBuffer`, `ArrayBuffer.isView`
• `mapValues`, `defaultTo` → `Object.fromEntries(Object.entries(o).map(...))`, `?? default`
• `deburr` → `s.normalize('NFD').replace(/\\p{Diacritic}/gu, '')`
• `sampleSize` → small util
• `memoize` → small WeakMap-based util (used in 3 places)

Tricky one: `lodash/template` is non-trivial to replace cleanly (used in `app/embed/Overrides.tsx` and `app/utils/packageHandle.ts`). Consider keeping just `lodash.template` as a focused dep, or write a small interpolator if the templates are simple.

Scope

• Add `catalog/app/utils/lodashReplacements.ts` with native versions of each helper.
• Replace 21 imports.
• Decide on `template`: keep `lodash.template` standalone, or replace.
• Remove `lodash` from `catalog/package.json`.

Effort

~2–3 hours.