chore(lint): add pine-motion stylelint rule banning hardcoded transition timing

[QuintonJason]

Description

Implementation-plan item #3 (part 2 of 2): a custom stylelint rule pine-design-system/no-hardcoded-motion that flags hard-coded time values in transition / transition-duration and points to the --pine-motion-duration-* tokens. Prevents new component transitions from drifting back to hard-coded timings after the migration in the parent PR.

Behavior & scope:

• Targets only transition / transition-duration. Keyframe animation durations (spinners, progress bars) are bespoke ongoing motion, intentionally out of scope.
• 0 / 0s / 0ms always allowed.
• Exact token matches (120ms/200ms/300ms and s forms) get a token suggestion and autofix (--fix rewrites 0.2s → var(--pine-motion-duration-base)).
• Off-grid values (e.g. 0.15s) report and must either use the nearest token or carry a justified stylelint-disable-next-line … -- <reason>.

The 5 existing off-grid micro-transitions (combobox ×3, multiselect, table — all 0.15s/0.1s) are annotated with documented disables, consistent with the behavior-preserving decision in the parent PR (these have no exact token; a follow-up can add 100/150ms tokens or retune them with design).

Stacked on #755 (style/adopt-motion-tokens), which migrates the exact-match transitions; landing the rule after the sweep keeps both PRs green. Mirrors the existing stylelint-plugin-pine-colors / -semantic-tokens plugins; registered under the same pine-design-system/ namespace; gated by the existing lint.styles → nx affected --target=lint job (no workflow changes).

New dependencies: none.

Fixes #(no-issue)

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• npx stylelint "src/**/*.scss" is clean (exit 0) with the rule active.

• Verified the rule fires on a fresh transition: opacity 0.2s ease and that --fix rewrites it to var(--pine-motion-duration-base).

• Verified off-grid 0.15s/0.1s lines report without a disable and pass with the documented disable.

• unit tests

• e2e tests

• accessibility tests

• tested manually

• other: rule run against the full SCSS surface + synthetic fixtures

Test Configuration:

• Pine versions: 3.26.x (docs/foundations lineage)
• OS: macOS 25.3.0
• Misc: stylelint ^14.13; tooling-only

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Design has QA'ed and approved this PR

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Note

Low Risk
Lint-only change plus comment annotations; no runtime or auth/data behavior changes.

Overview
Adds a Stylelint guard so new SCSS cannot use raw durations on transition / transition-duration, steering authors toward --pine-motion-duration-* (with --fix rewriting exact 120/200/300ms spellings to token vars). animation timings stay out of scope; zero durations are allowed; off-grid values must use a token or a justified disable.

libs/.stylelintrc.json registers stylelint-plugin-pine-motion.cjs and enables pine-design-system/no-hardcoded-motion.

Five existing 0.15s / 0.1s micro-transitions in combobox, multiselect, and table styles get stylelint-disable-next-line comments so the tree stays green until those timings are retokenized or retuned.

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[pixelflips]

Ran check locally and nothing was found. LGTM! 👍🏼