feat(practice): per-ring guided hints, Ring-N-of-M progress, and retry mechanic

Description

MapDefinition gains optional per-ring hint text to guide players in Practice Mode. The HUD shows ring progress instead of a competitive score bar. Players can retry instantly via teleport and state reset.

Acceptance Criteria

• MapDefinition JSON ring entries accept an optional `hint` string field (e.g. `{"id": 1, "type": "STANDARD", "hint": "Fly through the green ring!"}`)
• Absent `hint` fields are deserialized as `null` / `Optional.empty()` — no validation error
• In Practice Mode, entering a ring with a non-null hint displays the hint as an action bar or title message
• Hint display duration is configurable (default: 3 seconds)
• HUD shows ring progress as `Ring N of M` instead of the competitive score bar in Practice Mode
• A retry action (command or item interaction) teleports the player to the map spawn point
• On retry, all ring-tracker state is reset (rings completed = 0, timer = 0)
• No world reload occurs during retry — pure state reset + teleport
• Gson adapter (`RingEntryAdapter`) handles absent `hint` field gracefully
• Unit tests cover: hint deserialization (present, absent, null), HUD switch, retry state reset

Technical Details

• `hint` is stored in the ring DTO/record (e.g. `RingEntry`); existing entries without `hint` remain valid JSON
• `RingEntryAdapter` lives in `adapter` subpackage, is `final`, follows Gson Adapter naming convention
• `HudComponent` gains a `mode` discriminator or Practice-specific fields (record, compact constructor validates)
• Retry state reset must invoke the same ring-tracker initialization path used at map start

Dependencies

• #172 (Practice Mode session — HUD and retry only activate under `GameMode.PRACTICE`)

Estimate

M

Start by reading dependency #172, then inspect the RingEntry DTO, final RingEntryAdapter in the adapter subpackage, HudComponent, and the ring-tracker initialization path mentioned in the issue. Trace how Practice Mode enters rings and how retry actions are handled. Done means optional hints deserialize safely, Practice HUD progress and configurable display work, retry teleports without a world reload, and the listed unit tests pass.