feat(driver): serve compact rule metadata in the lint result

[e54-bot]

Summary

Implements option C from #431: lint no longer inlines the full lintRules response.

• wright lint --format json and the agent {"op":"lint"} result now carry rules as a compact [{"id", "effectiveSeverity"}] list — enough to interpret a finding's code and severity. Summary, rationale, documentation, known limits, evidence, and tags are served once by lintRules, which remains the authoritative full-metadata surface.
• wright-agent/v1 schema: LintResult.rules items move from LintRule to a new LintRuleSummary definition; LintRulesResult keeps LintRule.
• docs/cli/machine-contract.md gains the wright-result/v1 evolution policy the issue asked for (same additive-only rule as wright-agent/v1), with this reduction recorded as the approved exception ahead of the 1.0 freeze (Roadmap to v1.0: stable Workshop tooling platform #134).
• docs/cli/lint.md, docs/cli/commands.md, docs/agent-contract.md, and SPEC-99 updated to match the shipped shape.

Measurement (issue fixture overpy-pixelart.ws, zero findings)

Field	Before	After
result.rules	7455 B (78%)	368 B
envelope total	9586 B	1912 B

Contract note

This is the owner-approved exception named by #431: a field reduction inside wright-result/v1 and the lint agent operation, deliberately made before the envelope freezes at 1.0 rather than via a wright-result/v2.

Test plan

• cargo fmt --all -- --check, git diff --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --all-targets --all-features — all green, including agent_v1_schema_covers_every_advertised_request_and_response (schema-validates live lint/lintRules results)
• wright lint --format json on tests/fixtures/workshop/real-world/overpy-pixelart.ws — rules block 7455→368 B, findings unchanged
• New assertions pin the boundary: lint rules carry no prose fields; lintRules still serves summary et al.; --disable-rule still reported via config

Closes #431

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