Document dispatch entity path base

[clkao]

Clarify dispatch entity path resolution so operators can use split-root workflows without guessing the correct path base.

What changed

• Document caller-relative entity paths in built-in dispatch help.
• Mirror path semantics in the machine-readable dispatch schema.
• Add behavioral and schema tests for split-root resolution.

Evidence

• Go package suites: 17/17 passed in standard and race modes.
• Live probes: 3/3 path-resolution variants matched expected behavior.

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