chore: Upgrade to eslint 9

[rogaldh]

Description

PR introduces migration to eslint@9

⚠️ Depends on #899

Type of change

• Other (please describe): chore update

Screenshots

n/a

Testing

All CI tasks should pass

Related Issues

HOO-379

Checklist

• My code follows the project's style guidelines
• I have added tests that prove my fix/feature works
• All tests pass locally and in CI
• I have run build:info script to update build information
• CI/CD checks pass

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[greptile-apps]

Greptile Summary

This PR migrates the project from ESLint 8 (legacy .eslintrc.json) to ESLint 9 (new flat eslint.config.mjs), upgrades typescript-eslint from v6 to v8 (unified monorepo package), bumps eslint-config-next from v14 to v15, removes the @solana/eslint-config-solana shared config (now replaced by explicit rule declarations), and upgrades TypeScript from 5.3 to 5.5.

Key changes:

• New flat config uses FlatCompat to bridge the legacy next/core-web-vitals config, then layers js.configs.recommended and tseslint.configs.recommended on top with well-structured per-glob overrides.
• sort-keys-fix/sort-keys-fix is now an explicit error rule (previously inherited from @solana/eslint-config-solana); config/tooling files are correctly exempted via the *.config.* / *.mjs / *.cjs glob.
• Unnecessary eslint-disable comments are cleaned up across ~30 files, enabled by reportUnusedDisableDirectives: 'warn' in the new config. The removals are all justified: @typescript-eslint/no-redeclare (the type Foo = Infer<typeof Foo> pattern is now natively handled), @typescript-eslint/no-non-null-assertion (explicitly turned off globally), and react-hooks/exhaustive-deps disables in cluster.tsx and RawInputCard.tsx (the deps arrays were already complete).
• lint script changes from next lint (which only lints specific directories by default) to eslint . with explicit ignores; this broadens coverage to all project files.
• Minor: the @typescript-eslint/no-require-imports: 'off' override unnecessarily lists *.mjs alongside *.cjs/*.js — .mjs files can't use require() by design, so this is a no-op but slightly misleading.

Confidence Score: 5/5

• This PR is safe to merge — it's a tooling-only change with no runtime impact on the application.
• All changes are confined to linting configuration, dependency versions, and cleanup of now-redundant eslint-disable comments. The new flat config is well-structured with appropriate per-glob overrides. Every removed disable comment has a clear and correct rationale (rule turned off, first-of-duplicates, stable useReducer dispatch, complete deps arrays). The single P2 comment on *.mjs in the no-require-imports override has zero runtime impact.
• No files require special attention; the only note is the minor *.mjs inclusion in the no-require-imports override in eslint.config.mjs.

Important Files Changed

Filename	Overview
eslint.config.mjs	New ESLint 9 flat config replacing .eslintrc.json; introduces sort-keys-fix, tseslint v8 rules, and proper overrides for test/config/script files. One minor broadness concern with the *.mjs glob in the no-require-imports override.
package.json	Upgrades eslint 8→9, eslint-config-next 14→15, typescript-eslint monorepo package 6→8, removes @solana/eslint-config-solana, adds @eslint/eslintrc, @eslint/js, globals, sort-keys-fix plugin, bumps TypeScript 5.3→5.5. lint script changed from next lint to eslint .
.eslintrc.json	Deleted – legacy ESLint 8 config replaced by eslint.config.mjs.
app/utils/programs.ts	Removes the now-redundant eslint-disable from the PYTH_DEVNET enum member (first occurrence; only subsequent duplicates TESTNET/MAINNET need suppression).
app/providers/cluster.tsx	Removes react-hooks/exhaustive-deps suppress comment; dispatch from useReducer is stable so the deps array [cluster, customUrl] is correct.
app/components/inspector/RawInputCard.tsx	Removes react-hooks/exhaustive-deps suppress; rawInput.current is a ref (intentionally omitted), [value, onInput] are the actual reactive deps – correct.
app/components/instruction/lighthouse/tests/LighthouseDetailsCard.test.tsx	Removes @typescript-eslint/no-non-null-assertion from inline disables across ~20 sites, since the rule is now globally off in the new config. Non-null assertions with ! remain and are still valid TypeScript.
sentry/config.mjs	Removes the sort-keys-fix disable on the webpack key in createSentryBuildConfig(); keys are already in alphabetical order (org, project, silent, telemetry, webpack, widenClientFileUpload) so the comment was unnecessary.
tailwind.config.ts	Removes eslint-disable/enable block around screens object; the file now matches .config. glob in the new flat config's sort-keys override, so the inline disables are no longer needed.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[ESLint 8 – .eslintrc.json] -->|deleted| B[ESLint 9 – eslint.config.mjs]

    subgraph OLD["Old config (ESLint 8)"]
        A
        A1["extends: next/core-web-vitals\n@solana/eslint-config-solana"]
        A2["plugins: testing-library\nsimple-import-sort\neslint-comments"]
        A3["overrides: test files\nmock files\nscripts\nsentry imports"]
    end

    subgraph NEW["New flat config (ESLint 9)"]
        B
        B1["FlatCompat → next/core-web-vitals"]
        B2["tseslint.configs.recommended\njs.configs.recommended"]
        B3["plugins: simple-import-sort\nsort-keys-fix\neslint-comments\ntesting-library"]
        B4["Overrides: *.cjs/js/mjs (require)\ntest files (testing-library)\nmocks (unlimited-disable)\nlogger/scripts (console)\n*.config.* (sort-keys-off)\napp/** (sentry imports)"]
    end

    B --> B1
    B --> B2
    B --> B3
    B --> B4

    C["lint script: next lint → eslint ."] --> B
    D["typescript-eslint v6 → v8\n(monorepo package)"] --> B
    E["@solana/eslint-config-solana removed\nsort-keys-fix added explicitly"] --> B

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[askov]

thought: I thought it should match the next version, but it seems to work just fine. I'm a bit concerned about potential false positives