feat(mcp): expose STRATEGY.md / STATE.json via 5 new MCP tools

[hyoshi]

Summary

Add 5 MCP tools that expose mureo's context layer (STRATEGY.md and STATE.json) so MCP hosts without filesystem access can read and update strategic context:

Tool	Purpose
mureo_strategy_get	Read STRATEGY.md as markdown
mureo_strategy_set	Atomically replace STRATEGY.md (validates via parse_strategy)
mureo_state_get	Read STATE.json as a parsed v2 doc
mureo_state_action_log_append	Atomically append an action_log entry
mureo_state_upsert_campaign	Atomically upsert a CampaignSnapshot

Why now

• Claude Desktop chat / claude.ai web have no Read tool — without these MCP tools, users have to paste STRATEGY.md / STATE.json into chat manually.
• Meta's official MCP has shipped; Google's is likely next. When raw API access becomes a commodity, mureo's value sits in the orchestration layer (strategy + state + action_log + rollback + synthesis). That layer needs its own MCP surface so mureo isn't invisible from non-Code hosts.
• This is Phase 1 of the MCP-ization plan — Phase 2 (skill migration) and Phase 3 (synthesis tools) come later.

Security

• _resolve_path refuses any path that resolves outside cwd, mirroring mureo/mcp/_handlers_rollback.py:_resolve_state_file. Path.resolve() follows symlinks, so a STRATEGY.md inside cwd that symlinks to /etc/passwd resolves to the target and is rejected.
• All writes go through pre-existing atomic helpers in mureo.context.state / mureo.context.strategy (temp file + os.replace). A failed write leaves the original file intact (covered by test_strategy_set_is_atomic).
• mureo_strategy_set round-trips input through parse_strategy() so a malformed payload raises before the file is overwritten.

Test plan

• tests/test_mcp_tools_mureo_context.py — 13 unit tests covering all 5 tools, including atomic-write failure, missing-file defaults, required-field validation, upsert-create + upsert-update, and the path-traversal refusal.
• tests/test_mcp_tool_name_spec.py — regression guard updated to include tools_mureo_context; all 5 names match ^[a-zA-Z0-9_-]{1,64}$.
• tests/test_mcp_server.py::TestListTools::test_list_tools_returns_all_tools — total tool count updated 173 → 178.
• ruff check, black --check, mypy --strict all pass on new files.
• python-reviewer agent: addressed HIGH (unify path-resolve gate with rollback's relative_to idiom) and MEDIUM (drop redundant default in handle_state_get, add upsert-update test).

Out of scope

Pre-existing test failures in tests/test_mcp_tools_meta_ads_* and 4 tests in test_mcp_server.py (BYOD demo data leaking into expected "no credentials" assertions) are unrelated to this change and exist on the branch base.