Task: update formal docs (SRS/SDS) to reflect current implementation

[abitofhelp]

Summary

The formal documentation (SRS and SDS) is stale. Several items marked as "Future" are now implemented, and the API has been rewritten from generic-instantiation packages to an enum-indexed declarative parser.

Specific Gaps

SRS (Software Requirements Specification)

• REQ-CMD-001, REQ-CMD-002, REQ-CMD-003 are marked "Future" but command/subcommand support is implemented (enum-indexed `Command_Id` type, command-scoped flags, two-phase parse).
• Requirements should reflect the current enum-indexed API (`Command_Id`, `Flag_Id`, `Option_Id`, `Positional_Id` generic formals).
• The old generic-package API (Clara.Application, Clara.Flag, Clara.Option) is no longer the architecture.

SDS (Software Design Specification)

• Section 6 "Future Extensibility" discusses command support as future — it is now present.
• The design should document the enum-indexed architecture: `CLI_Config` aggregate, `Parse_Result` record, `Parse_Outcome.Result` return type.
• Document the two-phase parse approach (identify active command, then process scoped flags).

Acceptance Criteria

• SRS requirements reflect current implementation (no "Future" items that are done).
• SDS architecture matches the enum-indexed declarative parser design.
• No stale API references to the old generic-package approach.