[ychae517]

Description

Adds a new turn by turn directions format to replace the raw turn angle. Each step has an enum type that maps directly to an instruction the frontend shows, so the FE doesn't have to interpret angles without knowing what other branches exist. Types only; mock data comes in a follow-up PR.

Format

Directions is an ordered array of DirectionStep, a discriminated union on type:

type	extra fields	meaning
depart		start walking (always first)
turn	direction: slight_left | left | sharp_left | slight_right | right | sharp_right	turn at an intersection or a sharp enough bend
continue		go straight where another branch could be mistaken for the route
cross	street: string | null	cross a street
arrive		end of the walking path (always last)

Every step also has path_index (index into path_coords), distance (meters until the next step), onto (street/path name after the step, or null), and landmark (nearby landmark, or null).

The enums can be extended as the algorithm improves; the FE should fall back to a generic instruction for values it doesn't recognize.

Type of Change

• New feature (feat)

Changed Files

• src/walking/directions.ts (new)
  • Zod schemas + inferred types: TurnDirection, DirectionStep, DirectionStepType, Directions
• test/directions.test.ts (new)
  • Unit tests: valid directions parse, invalid steps are rejected, JSON schema generates

Related Issues

Part of #97 (step 1: types)

Does your code rely on another PR

No

Testing Done

Vitest:

• new tests added: test/directions.test.ts (13 tests, all passing)
• tsc --noEmit and typedoc --treatWarningsAsErrors pass locally

Checklist

• Commit messages follow Conventional Commits
• PR title follows <type>(scope): short description
• PR target branch is not main and is our current working update branch (e.g. maizebus2.1, dev)
• No print() / debugPrint() / console.log() left in production code
• Secrets / keys not committed