feat(mcpkit)!: deferred tool registration + Risk/Group primitives (MC-43)

[jgangemi]

• add mcpkit.Risk (ReadOnly/Write/Destructive), a required positional AddTool param that fail-closes on unannotated write/destructive tools
• auto-derive ToolAnnotations from Risk via mcpx.RiskAnnotations (MC-42) when the caller left Annotations nil; an explicit Annotations still wins
• add mcpkit.Group(name) ToolOption, arbitrary per-tool bookkeeping consumed by the registry's byGroup map
• defer tool registration out of AddTool into an unexported registry of pendingTool closures; App.finalize (called once, idempotently, from Run/Connect/HTTPHandler) registers every pending tool against the live mcpx.Server
• this is the load-bearing MC-43 step of the MC-40 tier/gate epic: it introduces the deferred-registration seam a later gate (MC-44) will filter before anything registers, but MC-43 itself is behavior-preserving -- every tool still ends up registered, just at Run/Connect/HTTPHandler time instead of at New
• update every AddTool caller (mcpkit_test.go, testkit/harness_test.go, examples/server, examples/minimal, examples/http) to pass an explicit Risk; all are ReadOnly query/demo tools

BREAKING CHANGE: AddTool now requires a Risk argument and registers tools at Run/Connect/HTTPHandler instead of at New.

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com

[coveralls]

Coverage Report for CI Build 29206278140

Coverage increased (+0.07%) to 95.934%

Details

• Coverage increased (+0.07%) from the base build.
• Patch coverage: 1 uncovered change across 1 file (50 of 51 lines covered, 98.04%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
mcpkit.go	51	50	98.04%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	1402
Covered Lines:	1345
Line Coverage:	95.93%
Coverage Strength:	1.11 hits per line

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💛 - Coveralls