docs/tests: finalize canonical CLI contract after PR #43

[axisrow]

Summary

Finish issue #42 based on the current post-PR #43 state.

direct-cli should keep the canonical-only CLI surface introduced by #43, and complete the remaining documentation/test work so the transport contract is explicit, stable, and owned by direct-cli.

Decision

• keep canonical names as the only primary CLI surface
• do not restore removed historical aliases by default
• allow compatibility aliases only by explicit exception when a concrete legacy syntax from tapi-yandex-direct must still be supported
• document dynamicads update as a transport gap until it is actually implemented

Required work

• document canonical command shape: direct <group> <command> [flags]
• add explicit naming rules for groups and commands
• state that direct-cli owns the public naming contract
• clarify that tapi-yandex-direct influences implementation, not public naming policy
• add canonical examples for:
  • changes check-campaigns
  • changes check-dictionaries
  • keywordsresearch has-search-volume
  • negativekeywordsharedsets
  • smartadtargets
  • dynamicads
• add README regression coverage for canonical examples and naming rules
• document dynamicads update as an unsupported transport gap

Acceptance criteria

• README is decision-complete about canonical transport naming
• no historical aliases are presented as active CLI contract
• help tests and README tests agree on canonical-only surface
• dynamicads update is explicitly documented as a gap

[axisrow]

Closing as completed. Verified the current tree already satisfies the issue #44 acceptance criteria: README documents the canonical-only CLI contract and ownership, canonical examples cover changes/keywordsresearch/negativekeywordsharedsets/smartadtargets/dynamicads, historical aliases are tested as removed, and dynamicads update is documented as unsupported by API. Verification: python3 -m pytest tests/test_cli.py tests/test_transport_contract.py -> 21 passed.