feat(routes-f): add sudoku, country lookup, csv parser, and mime lookup APIs

[Themancalledpg]

Description

Implements four new scoped routes-f APIs in one PR: sudoku grid validation, country info lookup, CSV parsing (RFC 4180 quote handling), and MIME lookup with reverse mapping and suggestions.

Closes #655
Closes #665
Closes #660
Closes #664

Changes proposed

What were you told to do?

Add four new endpoints under app/api/routes-f/ only, each with route logic and tests, and keep the implementation fully self-contained within that folder.

What did I do?

Sudoku validator (/api/routes-f/sudoku)

• Added POST endpoint to validate 9x9 sudoku grids with row, column, and 3x3 box duplicate detection.
• Returns { valid, complete, conflicts } where complete is true only when grid is full and valid.
• Rejects malformed grids with 400.
• Added tests for valid complete, valid partial, and each conflict type.

Country lookup (/api/routes-f/country)

• Added GET endpoint for ?code= and ?name= lookups, plus list-all when no params are provided.
• Added bundled dataset of 60 countries inside the route folder.
• Supports case-insensitive lookups by alpha2, alpha3, numeric code, and partial name.
• Returns required country fields including flag_emoji.
• Added tests for all lookup modes and partial matching.

CSV parser (/api/routes-f/csv-parse)

• Added POST endpoint with csv, optional has_header (default true) and delimiter (default ,).
• Implemented inline parser (no CSV library) supporting quoted fields, escaped quotes, and embedded newlines.
• Added numeric auto-coercion and 10MB input cap.
• Rejects ragged rows with 400 and offending row indexes in the error message.
• Added tests for quotes, embedded newlines, custom delimiter, and ragged rows.

MIME lookup (/api/routes-f/mime)

• Added GET endpoint for lookup by ?extension= or ?mime=.
• Bundled 179 MIME mappings with required categories in-folder.
• Unknown lookups return 404 with suggestions.
• Added tests for both lookup directions and common MIME types.

Check List (Check all the applicable boxes)

• My code follows the code style of this project.
• This PR does not contain plagiarized content.
• The title and description of the PR is clear and explains the approach.
• I am making a pull request against the main branch (left side).
• My commit messages styles matches our requested structure.
• My code additions will fail neither code linting checks nor unit test.
• I am only making changes to files I was requested to.

Screenshots / Testing Evidence

Did not run tests per request. Verification performed via code-level checks for scope, required response shapes, dataset counts, and endpoint behavior coverage in added unit tests.

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