[skip deploy] Specify exclusive end for Calendar CLI mutations

[pocketsharkk]

What changed

• add the decision-complete implementation spec for Exclusive End across Calendar CLI mutations
• link the spec from the README roadmap
• synchronize the CLI glossary with the canonical Calendar terms used by the contract

Why

event add and event set currently interpret all-day --end as inclusive, while the API, ICS, output, and event occurrence set use Exclusive End. The spec defines the v0.7 migration, cross-repository source ownership, rollout, rollback, validation, and implementation handoff without implementing the behavior.

Impact

Documentation only. No runtime, generated output, API surface, workflow, or deployment behavior changes in this PR.

WSPC Todo: tod_01M006KX9VBKKM8Y43SNNJZM4T

Validation

• git diff --cached --check
• verified the spec has exactly the six required top-level sections
• verified the README roadmap link and glossary _Avoid_ entries
• confirmed the diff contains only CONTEXT.md, README.md, and the new spec

Remaining acceptance

None.