feat(sdk): v0.28.0 release housekeeping (Sprint 55 T1)

[dp-web4]

Summary

• Version bump 0.27.0 → 0.28.0 consolidating post-Sprint-53 work
• CHANGELOG entry for cross-society MCP types (PR feat(sdk): cross-society types — CrossSocietyContext, ReputationEnvelope, MCPContextResource #195/test(sdk): add coverage for #195-landed cross-society types #199), conformance xfail resolution (PR fix(conformance): reconcile 3 vectors with normative spec — resolve 3/8 xfails #210)
• All documentation counters reconciled: 369→376 exports, 2709→2749 tests, 8→5 xfails, 6→7 error categories
• Bug fix: _pkg_version("web4") → _pkg_version("web4-sdk") — stale egg-info from pre-rename was returning old version
• Sprint 54 (retroactive C-series entry) + Sprint 55 added to SPRINT.md
• SESSION_FOCUS.md fully refreshed (was stale since Sprint 53)

Quality gates

• 2749 passed, 5 xfailed (conformance gaps, pre-existing, operator-blocked)
• mypy --strict: 0 errors across 26 source files
• ruff check: 0 errors
• CLI info: web4 0.28.0 / Modules: 23 / Exports: 376 / Schemas: 12
• CLI selftest: OK: 23 modules, 12 schemas, 23 types roundtripped
• GitNexus detect_changes: risk level LOW, 0 affected processes

Files modified (9, 0 new)

• pyproject.toml — version bump
• CHANGELOG.md — v0.28.0 entry
• web4/__init__.py — counters + pkg_version fix
• README.md — version, counts, error categories
• examples/quickstart.py — docstring version
• tests/test_cli.py — version assertions
• tests/test_package_api.py — version assertions
• docs/SPRINT.md — Sprint 54 + 55 entries
• SESSION_FOCUS.md — full refresh

Test plan

• python -m pytest tests/ -q — 2749 passed, 5 xfailed
• mypy --strict web4/ — clean
• ruff check web4/ tests/ — clean
• python -m web4 info — reports 0.28.0
• python -m web4 selftest — OK
• python examples/quickstart.py — runs successfully

🤖 Generated with Claude Code

[dp-web4]

APPROVED: Sprint 55 T1 v0.28.0 release housekeeping. Independently verified on the branch: python -m web4 info → 0.28.0 / 23 modules / 376 exports / 12 schemas (matches claim exactly); selftest OK (23 modules, 23 roundtrips); test_cli.py + test_package_api.py 163 passed. The _pkg_version("web4")→_pkg_version("web4-sdk") fix is a correct stale-egg-info bug fix. Version bumped consistently across pyproject/README/quickstart/init/test assertions. The large SESSION_FOCUS.md trim (−225) removes per-sprint detail that the file's own header designates SPRINT.md as the source of truth for — correct de-duplication, not lost content (history preserved in SPRINT.md). 9 files, 0 new. Development-phase housekeeping with a sprint-task reference: aligned, no drift.