refactor(cli): narrow arkenv check and drop custom dotenv AST formatting parser

[yamcodes]

Summary

Narrow arkenv check to its core mandate: validating runtime environment variables (process.env + overlays) against the declared TypeScript schema.

Remove internal .env AST formatting and syntax lint checks from packages/arkenv/src/features/check. File-level formatting, unquoted space detection, and syntax linting belong in dedicated ecosystem tools (e.g. dotenv-linter).

This supersedes ADR 0017 and aligns with the archived arkenv lint RFC in Discussion #1710.

Proposed Changes

1. Simplify Dotenv Loading in features/check:
   • Strip custom AST coordinate tracking and formatting/syntax lint diagnostics.
   • Use standard key-value dotenv parsing solely to populate values for schema validation.
2. Lock arkenv check Mandate:
   • arkenv check reports errors only when runtime values fail schema validation or required keys are missing.
3. Update ADR 0017:
   • Mark docs/adr/0017-dotenv-linter-custom-parser-strategy.md as Superseded / Rejected in favor of focused runtime validation.
4. Changeset:
   • Add a changeset for arkenv.

Acceptance Criteria

• arkenv check runs schema validation on resolved environment variables without running custom AST formatting checks.
• ADR 0017 status is updated to Superseded.
• All arkenv check tests pass (pnpm test).
• Changeset is included for arkenv.

Out of Scope

• Removing --env-file overlay support from arkenv check.
• Implementing arkenv lint (archived to Discussion RFC: (Dev-time .env file linter) #1710).

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[yamcodes]

This was generated by AI during triage.

Agent Brief

Category: enhancement
Summary: Narrow arkenv check to runtime value validation against schemas and drop custom dotenv AST syntax/formatting linter checks.

Current behavior:
The check feature includes custom dotenv parsing logic designed to track AST coordinates and report syntax errors or formatting diagnostics for .env files.

Desired behavior:
arkenv check parses dotenv files solely to populate the environment record for schema validation. It does not perform file-level syntax or whitespace linting. ADR 0017 is updated to Superseded.

Key interfaces:

• Dotenv loader in features/check - simplify to load key-value pairs without coordinate tracking or lint diagnostics.
• docs/adr/0017-dotenv-linter-custom-parser-strategy.md - update Status to Superseded.

Acceptance criteria:

• Dotenv loading in arkenv check only feeds runtime values into schema validation.
• ADR 0017 document status updated to Superseded.
• All arkenv check test suites pass cleanly (pnpm test).
• Changeset is added for arkenv.

Out of scope:

• Removing --env-file overlay support from arkenv check.
• Implementing arkenv lint (archived to Discussion RFC: (Dev-time .env file linter) #1710).