feat(sema-policies): expand the standard policy pack

[HelgeSverre]

What changed

• add composable semantic subject constructors for file, network, command, and external-action controls
• add configurable input and evidence requirements
• add safe coding-agent and draft-only customer-support profiles
• add human-review, change-control, AI oversight, and employment-assistance profiles
• add independently authored reviewable-output, certainty-audit, and placeholder controls
• add composable deny-only profiles and stricter constructor validation
• document installation, approval semantics, evidence export, and known limitations
• bump sema-policies to 0.2.0

Why

Issue sema-lisp/sema#50 calls for an installable standard policy pack built from deterministic runtime controls. The Sema runtime now supports semantic policy subjects, deterministic content/output checks, completion evidence, durable signed approval gates, and evidence export, so these reusable policies can be shipped without embedding them in core.

This PR intentionally does not claim automatic action-bound approval, semantic fact checking, conditional model routing, or regulatory compliance. Those need additional runtime support or human judgment.

Depends on sema-lisp/sema#143 and the policy runtime work it is stacked on.

Validation

• sema fmt --check package.sema tests.sema
• sema --no-llm tests.sema (9/9 tests)
• package profiles compile against the issue #50 Sema branch