feat: add JSON output to purge command (12.12)

[josecelano]

Summary

Implements roadmap task 12.12 — adds --output-format json support to the purge command.
Closes #394.

Changes

New files

• src/presentation/cli/views/commands/purge/mod.rs — module with re-exports
• src/presentation/cli/views/commands/purge/view_data/purge_details.rs — PurgeDetailsData { environment_name, purged } with from_environment_name() constructor
• src/presentation/cli/views/commands/purge/views/json_view.rs — JsonView::render() → pretty-printed JSON
• src/presentation/cli/views/commands/purge/views/text_view.rs — TextView::render() → "Environment '…' purged successfully"

Modified files

• src/presentation/cli/views/commands/mod.rs — added pub mod purge;
• src/presentation/cli/controllers/purge/handler.rs — added output_format: OutputFormat to execute(), updated complete_workflow() to dispatch via Strategy Pattern
• src/presentation/cli/dispatch/router.rs — Commands::Purge arm reads context.output_format() and passes it to the controller
• docs/user-guide/commands/purge.md — added JSON output section with examples
• docs/issues/394-add-json-output-to-purge-command.md — marked all goals and checklist items as complete
• project-words.txt — added checkmark to avoid cspell false positive

JSON Output Format

{
  "environment_name": "my-env",
  "purged": true
}

purged is always true on the success path — failures exit with a non-zero code and produce no JSON output.

Testing

• All 2282 existing tests pass (cargo test --lib)
• Unit tests added for PurgeDetailsData, JsonView, and TextView
• Full linter suite passes (cargo run --bin linter all)
• cargo machete — no unused dependencies

Notes for Manual Verification (Phase 5)

Before merging, a user with an existing environment can verify both outputs:

# Text (default)
cargo run -- purge <env> --force

# JSON
cargo run -- purge <env> --force --output-format json 2>/dev/null

Expected JSON:

{
  "environment_name": "<env>",
  "purged": true
}

[josecelano]

ACK fa8c998