Add domain-scenario Gherkin tags to all A2A, session, and CLI feature
files (30 files) so tests can be filtered individually via behave.
- 8 A2A feature files: @a2a tag
- 7 session feature files: @session tag
- 15 CLI feature files: @cli tag
ISSUES CLOSED: #9124
Renamed src/cleveragents/acp/ to src/cleveragents/a2a/ and all 13
Acp* classes to A2a* per ADR-047 (A2A Standard Adoption). Updated
all imports, structlog event names (acp.* → a2a.*), field names
(acp_version → a2a_version), and test references across the entire
codebase. This is a cosmetic rename only — no behavioral changes.
ISSUES CLOSED: #688