Add mockgrbl jog completion and limit rejection tests

[ianbruene]

Motivation

• Extend the existing Linux-only mockgrbl_e2e integration suite to cover two high-value jog behaviors: natural JogTo completion at a target and out-of-bounds JogTo rejection without starting motion.
• Keep changes scoped to the integration test package and small test helpers so tests remain CI-safe, do not require UI or hardware, and avoid timing fragility.

Description

• Add TestDDGoJogToEndpointCompletesAgainstMock which issues controller.JogTo(ctx, "X", -1.0, 60), waits for the mock to reach Idle with no active move/queue and machine X near -1.0, then verifies the DDGo controller snapshot matches the completed position.
• Add TestDDGoJogLimitRejectionAgainstMock which issues an out-of-bounds controller.JogTo(ctx, "X", -999.0, 60), asserts the mock remains Idle with no motion and machine X near the baseline, and verifies the mock emitted a jog-limit response like [MSG:jogLIM] / error:15.
• Introduce small test helpers: typed mockLogEntry, shared tolerance posTol, generic getJSON/fetchJSON helpers, responses/events accessors, richer dumpDiagnostics, and bounded polling helpers waitForMockState and waitForControllerState that avoid fixed long sleeps and provide last-state diagnostics on timeout.
• Preserve existing constraints: tests remain under the linux && serial && mockgrbl_e2e build tags, use the real serial transport via the harness, and do not modify mockgrbl or production controller behavior.

Testing

• Ran go test -tags 'serial mockgrbl_e2e' ./internal/integration/mockgrbl and the integration tests passed.
• Ran go test ./... and the full test suite passed.
• Ran go test -tags serial ./internal/transport ./internal/ports ./internal/app ./internal/grbl and those package tests passed.

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Codex Task