office: add TurtleTerm operator flows

[mdheller]

Summary

Adds the first TurtleTerm Office operator surface without implementing an office suite inside TurtleTerm.

The new office / /office flow produces deterministic SourceOS Office operator plans that point at sourceosctl office, include the TurtleTerm receipt command, and summarize OfficeArtifactEvidence runtime contract IDs when evidence is present.

Changes

• Adds turtle-term office plan.
• Adds /office plan alias support.
• Adds turtle-term office evidence inspect <path>.
• Emits operator-plan JSON with:
  • sourceos.turtleterm.office.operator_plan.v0
  • command_argv for sourceosctl office ...
  • receipt_command for turtle-term run -- sourceosctl office ...
  • expected office runtime contract kinds.
• Emits evidence-summary JSON with:
  • sourceos.turtleterm.office.evidence_summary.v0
  • office document/version/writeback IDs when present.
• Adds smoke coverage for normal office flow, /office alias, and evidence summary.
• Updates README command examples and product surface list.

Boundary

No Google/Microsoft/Apple runtime dependency is introduced. TurtleTerm remains an operator/receipt surface and does not become the office runtime, WOPI host, or document engine.

Validation target

make turtle-smoke

The smoke target runs assets/sourceos/tests/test_sourceos_term_smoke.py and syntax checks packaging helpers.