105 broken redirect destinations in docs.json (onchainkit, smart-wallet, apps legacy paths)

## Description
While auditing `docs.json` redirects, I found many `destination` values that point to pages which no longer exist in the `docs/` tree. Visitors hitting these legacy URLs get redirected straight into a 404 instead of the intended page.

I verified this by cross-checking every redirect `destination` against the actual file tree and the `docs.json` navigation. Two of the highest-impact cases (75 redirects total) are already fixed in the companion PR:

- `/base-account/basenames/basenames-wagmi-tutorial` (39 redirects) -> now points to `/base-account/framework-integrations/wagmi/basenames`
- `/apps/quickstart/create-new-app` (36 redirects) -> now points to `/apps/quickstart/build-app`

## Remaining broken destinations (105 unique, ~270 redirect entries)
The biggest remaining groups, by number of redirects pointing at them:

| Count | Broken destination | Notes |
|---|---|---|
| 94 | `/get-started/migrate-from-onchainkit` | Itself redirects to `/onchainkit/migrate-from-onchainkit`, which also doesn't exist - a broken redirect chain. No `docs/onchainkit/` directory exists in this repo, though `README.md` and `claude.md` still list `onchainkit/` as an established section. Not sure if this content moved to a separate site/repo - needs maintainer input. |
| 13 | `/apps/introduction/overview` | No `docs/apps/introduction/` directory exists. Possibly should be `/apps` or `/apps/quickstart/build-app`. |
| 11 | `/smart-wallet/quickstart` | `smart-wallet` appears fully retired (superseded by `base-account`), same pattern as ~40 other `/smart-wallet/*` and `/base-app/*` destinations. |
| 5 | `/apps/core-concepts/manifest` | No `core-concepts` directory under `docs/apps/`. |
| 4 | `/apps/troubleshooting/how-search-works` | No `troubleshooting` directory under `docs/apps/`. |
| 4 | `/apps/featured-guidelines/design-guidelines` | No `featured-guidelines` directory under `docs/apps/`. |

The remaining ~90 unique destinations are mostly 1-3x each, largely `/onchainkit/*`, `/smart-wallet/*`, and `/base-app/*` legacy paths - consistent with a larger IA migration where redirect sources were kept but destinations were never updated to match final page locations.

## Why I'm not fixing these all in one PR
Several of these (especially the `/onchainkit/*` and `/smart-wallet/*` groups) look like they may map to content that was intentionally moved out of this repo entirely, rather than just renamed within it. Guessing destinations for ~270 redirect entries without confirming intent risks introducing new incorrect redirects. Flagging here so a maintainer can confirm whether:
1. OnchainKit docs moved elsewhere (and these redirects should point external), or
2. Should be removed/consolidated if that content is fully retired.

Happy to open follow-up PRs for whichever groups get confirmed.