feat(mcp): generative-UI MVP demo tools

[razeone]

Adds 7 read-only SQL Server MCP tools that feed the generative-UI demo flows (Performance Tuning, Health Audit, Schema Discovery).

Tools added

Performance

• top_queries — top-N by total worker time from sys.dm_exec_query_stats (capped 50)
• missing_indexes — sys.dm_db_missing_index_* ordered by improvement_measure (top 50)
• wait_stats — sys.dm_os_wait_stats with idle/system noise filtered (capped 50)
• blocking_sessions — blocked sessions from sys.dm_exec_requests with blocker/blocked logins

Discovery

• fk_graph — full FK graph (one row per FK column)
• column_stats — sys.stats + sys.dm_db_stats_properties for a given table

Health

• db_health_checks — 10 curated checks (auto_close, auto_shrink, recovery model, page verify, compat level, query store, last full/log backups, unused indexes, DBCC CHECKDB recency)

Safety

• All values bound via SqlParameter — never concatenated.
• Identifier args (column_stats) pass the existing SqlIdentifier allow-list AND an INFORMATION_SCHEMA existence check before being bracket-quoted.
• SqlException details are logged in full but only Number + first-line message reach the client.
• Per-check try/catch in db_health_checks so msdb / DBCC permission errors degrade to Info: skipped instead of failing the whole tool.
• All tools strictly read-only (SELECT / DMV reads).

Verification

• dotnet build src/CloudEngAgent.Mcp.Server ✅
• dotnet test tests/CloudEngAgent.Mcp.Server.Tests — 51/51 passed ✅
• dotnet build CloudEngAgent.slnx ✅

New tests cover identifier validation on column_stats, top-bounds on top_queries / wait_stats, and assembly-level discovery of all 7 tool names.