fix: type plugin API against Payload shapes instead of any

[jhb-dev]

Summary

Implements plan 012 (Option A — type-only Payload dependency) and a follow-up naming cleanup. No runtime behavior change.

fix: — type the plugin API against Payload's own shapes

• Removed all four eslint-disable @typescript-eslint/no-explicit-any headers in src/plugin/*.
• payload added as an optional peerDependency (^3.0.0) + pinned devDependency (3.84.1, matching the example app). Imports are type-only — nothing is added to the runtime bundle.
• index.ts / schemaApi.ts now use real Config, SanitizedConfig, Payload, PayloadRequest, Block, and the sanitized config types. contentCliPlugin is (config: Config) => Config; the schema-API functions take real PayloadRequest/Block. Consumers get type-checking + autocomplete.
• fields.ts takes Field[]/Record<string, Block> publicly and reads each field through a documented internal FieldView (nested fields/tabs/blocks keep their real Payload types so recursion stays checked).
• lexical.ts stays structural — RichTextField.editor is a payload-core type, so @payloadcms/richtext-lexical is never imported; the editor walk uses unknown + guards. Apps without the lexical package are unaffected.
• Tests are excluded from tsc; kept the strict signatures clean in the IDE via a typed mockReq return and thin loosened wrappers over the imported functions.

refactor: — replace non-descriptive short variable names

Renamed abbreviations like ep, c, cs, op, val, and single-letter callback params (f, s, b, l, o, n) to meaningful names across src and tests. Kept conventions (err/e for errors, i/j loops, a, b sort comparators, id, ms, rl).

Known cost

The published .d.ts now references Payload's type names, so a future Payload major reshaping Field/Config/PayloadRequest could surface a type error for consumers on that major until a compatible release ships.

Verification

• pnpm typecheck ✅ pnpm lint (0 warnings) ✅ pnpm format:check ✅
• pnpm test — 304 passed, 40 skipped (integration suite is env-gated on a running seeded example app)