feat(show): surface related traceability commands (trace/impact/who-verifies/refs) in show output

Summary

show <qname|id> prints an element's own fields and documentation, but nothing pointing at the traceability commands (trace, impact, who-verifies, refs) that already exist and answer the natural next questions about that same element. Add a short "Related" footer to show's output suggesting the applicable follow-up commands for the element's type, pre-filled with its id.

Motivation

trace, impact, who-verifies, refs, and connectivity already do real traceability-graph work — exactly the kind of thing that's expensive to reconstruct by hand (I found myself running grep -rl "REQ-MQTT-009" specification/ and manually cross-referencing PlanningItem/Requirement/TestCase files during a verification pass, when syscribe trace REQ-WEB-011 would have produced the same answer in one call). The commands aren't missing — they're just not surfaced at the moment they'd help, which is right after looking at the element itself via show. --agent-instructions documents them well up front, but that's a one-time read at the start of a session; there's nothing in the steady-state, per-command output that re-surfaces them mid-task.

For an LLM agent in particular, this matters more than it would for a human: a human skimming show's output has the CLI's --help a keystroke away and may already remember the command exists; an agent re-derives its next action from whatever's in front of it in that turn, and is much likelier to default back to grep/Read if the tool itself doesn't mention the shortcut.

Proposed shape

Append a short, type-appropriate footer to show's output:

$ syscribe show REQ-WEB-011
[... existing fields/documentation ...]

Related:
  syscribe trace REQ-WEB-011          full traceability slice
  syscribe who-verifies REQ-WEB-011   verifying TestCases
  syscribe impact REQ-WEB-011         downstream/upstream change impact
  syscribe refs REQ-WEB-011           inbound references

Only list commands that are meaningful for the shown element's type (e.g. who-verifies for a Requirement, not a PartDef; n2/connectivity for architecture elements). Suppressible with a flag (show --no-related) for scripting/piping contexts where the extra lines aren't wanted.

Acceptance criteria

• show on a Requirement suggests trace/who-verifies/impact/refs
• show on an architecture element (PartDef/Part) suggests impact/connectivity/n2/refs instead, not the requirement-specific ones
• --json output is unchanged (footer is text-mode only)
• --no-related suppresses the footer

Start at the existing show command and inspect how element types select behavior, how text and --json output are separated, and how command-line flags are defined. Verify the related-command footer for Requirements and architecture elements, confirm --no-related suppresses it, and ensure --json output remains unchanged.