Bump eslint 8.57 → 9/10.x and `@typescript-eslint` 5.62 → 8.x (eslint 8 is EOL, 2-3 majors behind)

[pinecone-groundskeeper]

Problem

The lint toolchain in package.json devDependencies is far behind and partially end-of-life:

• eslint is pinned ^8.33.0, resolving to 8.57.1 in package-lock.json. Latest is 10.8.0 (2 majors behind). Running npm ci in this repo prints: npm warn deprecated eslint@8.57.1: This version is no longer supported. Please see (eslint.org/redacted) for other options.
• @typescript-eslint/eslint-plugin and @typescript-eslint/parser are both pinned ^5.51.0, resolving to 5.62.0. Latest for both is 8.66.0 (3 majors behind).

These two are coupled: @typescript-eslint v6+ requires ESLint ^7.0.0 || ^8.0.0 as a peer at minimum, and current @typescript-eslint majors track current ESLint majors, so they need to move together rather than independently.

Note: ESLint 9 removed support for the legacy .eslintrc.* format (this repo currently uses .eslintrc.cjs) in favor of flat config (eslint.config.js) — landing this bump requires migrating the config file, and checking whether eslint-config-airbnb-base (used here) needs a compatibility shim (e.g. @eslint/eslintrc's FlatCompat) under flat config.

Acceptance criteria

• eslint is bumped off the unsupported 8.x line (9.x or 10.x).
• @typescript-eslint/eslint-plugin and @typescript-eslint/parser are bumped to a major compatible with the new ESLint version (8.x).
• The existing lint rule set (airbnb-base + prettier integration) is preserved under whatever config format the new majors require; npm run lint runs clean (or with the same pre-existing findings, not new ones) against src/.
• package-lock.json is regenerated to match.

Scope

Bump only eslint, @typescript-eslint/eslint-plugin, and @typescript-eslint/parser (and the config migration strictly required to keep them working, e.g. converting .eslintrc.cjs to flat config). Do not touch prettier (separate, independent devDependency) or change lint rules/behavior beyond what the major bumps require.

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