docs: list supported configuration file names

[tarikermis]

🔗 Linked issue

Closes #4505

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)

📚 Description

What: adds a "Supported configuration files" section to the Configuration docs page listing exactly which config files Nitro loads, and removes two documented claims that do not hold.

Why: as reported in #4505, the docs never stated which configuration file names are supported, making it impossible to tell whether e.g. .nitrorc.js, nitro.config.yaml, or .config/nitro.toml work.

Every listed filename/location was verified two ways:

1. In source: Nitro loads config via c12 (loadConfig/watchConfig with name: "nitro", cwd = the rootDir override, i.e. the CLI dir argument defaulting to the current working directory — src/config/loader.ts, src/cli/commands/build.ts). c12 (4.0.0-beta.5, resolveConfig in node_modules/c12/dist/index.mjs:324) resolves nitro.config → .config/nitro → .config/nitro.config (first match wins) with extensions .js/.ts/.mjs/.cjs/.mts/.cts/.json/.jsonc/.json5/.yaml/.yml/.toml, and always reads an extensionless .nitrorc (rc9 key=value syntax) from the same directory, merged with lower priority than the main file.
2. Empirically, by running Nitro's actual loadOptions() against temp directories containing each candidate file:
   • ✅ loaded: nitro.config.{ts,js,mjs,cjs,mts,cts,json,jsonc,json5,yaml,yml,toml}, .config/nitro.*, .config/nitro.config.* (same extensions), .nitrorc
   • ❌ not loaded: .nitrorc.{json,js,yaml}, .config/.nitrorc, package.json nitro key, ~/.nitrorc
   • precedence confirmed: root nitro.config.* > .config/nitro.* > .config/nitro.config.*; main config file > .nitrorc

Removed claims (both verified non-functional, not just undocumented):

• "Config from package.json" — c12 only loads the package.json key when its packageJson option is enabled, and Nitro never enables it (also true for Nitro v2's loader with c12 v2/v3, so this is a docs inaccuracy rather than a v3 regression).
• .nitrorc "in the user's home directory" — c12 only reads rc files outside the cwd when its globalRc option is enabled, which Nitro also never sets.

Note for maintainers (out of scope here): getConf in src/config/loader.ts:101 still reads rawConfigs.packageJson, which can never be populated — worth either enabling packageJson: true or dropping that read as a follow-up.

Checks run: pnpm lint (oxlint + oxfmt) ✅; docs pnpm build (undocs/Nuxt, 359 routes prerendered) ✅ with the new section present in the built output; empirical config-loading probe as described above ✅. Docs-only change, so no unit tests apply. The diff was reviewed by claude-opus-5 via kiro-cli (read-only); its findings (order-claim phrasing, rc directory precision, Vite inline-config mention) are incorporated.

Limitations: verified on Linux/Node 22 against main @ 52abde8; I did not test Windows path handling. The extension-level priority within one basename (c12 checks .js before .ts) is intentionally left undocumented as an edge case.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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ℹ️ Recent review info

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Reviewing files that changed from the base of the PR and between 58863e9 and 8bd3f3a.

📒 Files selected for processing (1)

• docs/1.docs/50.configuration.md

🚧 Files skipped from review as they are similar to previous changes (1)

• docs/1.docs/50.configuration.md

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📝 Walkthrough

Walkthrough

The configuration documentation now lists supported Nitro configuration filenames, lookup order, project-root resolution, .nitrorc precedence, and inline Vite options. It replaces generic c12 guidance and removes the package.json configuration section.

Changes

Configuration documentation

Layer / File(s)	Summary
Document configuration loading rules docs/1.docs/50.configuration.md	The guide defines supported configuration filenames, lookup order, project-root resolution, .nitrorc merging precedence, and inline Vite configuration.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Possibly related PRs

• nitrojs/nitro#4363: Expands supported Vite configuration file extensions used during configuration detection.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses the conventional commit format and accurately describes the documentation change.
Description check	✅ Passed	The description clearly explains the supported configuration files, removed inaccurate claims, and verification performed.
Linked Issues check	✅ Passed	The PR addresses issue #4505 by documenting supported filenames, extensions, lookup order, and unsupported variants.
Out of Scope Changes check	✅ Passed	The changes are limited to the configuration documentation requested by issue #4505.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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Actionable comments posted: 1

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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@docs/1.docs/50.configuration.md`:
- Around line 41-45: Update the configuration file lists in the Nitro
configuration documentation to reflect c12’s actual extension precedence,
placing JavaScript extensions before TypeScript extensions. Apply the same
ordering consistently to all three locations: nitro.config, .config/nitro, and
.config/nitro.config.

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Run ID: e4397044-9b7b-49a4-bfdd-2009d3845724

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📒 Files selected for processing (1)

• docs/1.docs/50.configuration.md