Clarify fast local validation

[zack-nova]

Summary

• Documents mise run check as the fast local feedback loop for day-to-day development.
• Keeps mise run ci documented as the full strict validation gate for review and landing.
• Adds validation parity checks for fast/strict task descriptions, cached Go test usage, and testing docs.

Linked Issue

Closes #120

Dev Brief Mapping

• A fast local command, such as mise run check or an equivalent task, is documented as the normal development feedback loop: contributor and maintainer testing docs now introduce mise run check for day-to-day development.
• The fast command uses cached Go tests where appropriate and avoids unnecessary full no-cache integration sweeps: tasks.check still runs test:go, not test:go:ci, and the parity test enforces that boundary.
• mise run ci remains the full strict validation command and still matches repository testing expectations: docs preserve mise run fix + mise run ci; tasks.ci still runs lint, no-cache Go tests, vuln, and shell validation.
• The difference between fast feedback and full strict CI is clear in task descriptions and contributor docs: mise.toml, contributor docs, and maintainer docs now use fast/full strict language.
• Release-surface changes still clearly require the release-surface validation path: contributor docs keep and reinforce sh ./scripts/test_release_surface_hyard.sh; validation parity checks the command remains documented.

What Changed

• Updated mise run check and mise run ci task descriptions.
• Added a Fast Local Feedback section to contributor testing docs.
• Added fast-vs-strict validation guidance to maintainer testing strategy.
• Extended scripts/test_validation_parity.sh to guard the documented validation contract.

Validation

• Command: sh ./scripts/test_validation_parity.sh
• Result: passed after RED/GREEN cycle
• Command: mise run fix
• Result: passed with temporary cache paths outside the repo
• Command: mise run ci
• Result: passed; lint reported 0 issues, Go tests passed, govulncheck found no called vulnerabilities, shell validation passed
• Command: mise run check
• Result: passed; fast path ran lint plus cached Go tests
• Command: sh ./scripts/test_release_surface_hyard.sh
• Result: passed; goreleaser config check skipped because goreleaser was not installed
• Manual verification: reviewed staged diff scope and git diff --check

Risk

• Low. This is documentation plus validation-guard coverage for existing task behavior.

Out of Scope

• Product command behavior changes.
• CI topology changes.
• Replacing mise as the local task runner.

Reviewer Notes

• TDD loop used: added failing parity assertions first, updated task descriptions/docs, then reran targeted and full validation.