Refactoring: clean codebase, improve generation quality, rewrite README

Context

Full audit of the codebase followed by three axes of improvement:
removal of dead code and unused dependencies, application of Rust idioms,
and improvements to the Docker Compose generation output.

The README has been rewritten to reflect the actual state of the project
instead of overpromising on "production-ready" capabilities.

What changed

Dead code elimination

• Deleted optimized_parser.rs (325 lines, entirely unused)
• Removed AthenaConfig, legacy structs in compose.rs, TemplateError variant,
  ValidationErrorType enum, NetworkMode enum, PullPolicy enum
• Removed all dead factory methods and unused fields across the codebase
• 36 #[allow(dead_code)] reduced to 0

Unused dependencies

• Removed uuid, anyhow, tempfile from main dependencies (none were imported)
• Added indexmap for deterministic service ordering

Rust idioms

• Replaced unwrap() in production code with get_or_insert_with
• Replaced byte-indexed string slicing with strip_prefix/strip_suffix
• Replaced format_push_string with write!/writeln!
• Applied inline format args across the codebase
• Replaced wildcard imports (use ast::*) with explicit imports
• Simplified should_be_verbose, execute_info, calculate_similarity,
  validate_build_args_against_dockerfile

Docker Compose generation

• Removed container_name from output (was blocking docker compose --scale)
• Removed pull_policy: missing (redundant, Docker's default)
• deploy.restart_policy is now only emitted when Swarm features are used,
  eliminating the conflict with the top-level restart: field
• Labels, networks and volumes use BTreeMap for deterministic ordering
• Services use IndexMap with topological sort (dependencies first)
• Auto-generated healthchecks for services with known image type and mapped port
• Project name lowercased in the name: field to match Docker conventions

README

• Rewritten from scratch with honest positioning
• Removed "production-ready" framing, replaced with "solid base with sane defaults"
• Shorter (200 lines -> 110 lines), factual, includes DSL reference table

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