Drop maximum_name_length; remove How-To-Use from Settings

[dadachi]

Mirrors NativeAppTemplate-Android PR #47. Two unrelated substrate-v2 cleanups bundled here.

1. Drop maximum_name_length from permissions; move to NatConstants

Android port of NativeAppTemplate-iOS#59. The server no longer sends maximum_name_length in /shopkeeper/permissions; the client already tolerated its absence via a default. Promote the value to a constant and drop the dead plumbing.

Stop reading maximum_name_length from /shopkeeper/permissions

• Meta: drop the @SerialName("maximum_name_length") field.
• Permissions: drop getMaximumNameLength() helper.
• UserData: drop maximumNameLength field.
• user_preferences.proto: reserved 23 (was maximum_name_length) so the wire number isn't reused.
• NatPreferencesDataSource: drop the read in the userData mapping, the write in setPermissions, and the getMaximumNameLength() flow.
• LoginRepository (interface + impl + DemoLoginRepository + TestLoginRepository): drop getMaximumNameLength().

Move maximumNameLength to NatConstants

• NatConstants: add MAXIMUM_ITEM_TAG_NAME_LENGTH = 100.
• ItemTagCreateViewModel + ItemTagEditViewModel:
  • UiState.maximumNameLength default now reads the constant.
  • Drop the loginRepository constructor param — it was only used for getMaximumNameLength().
  • ItemTagCreateViewModel.reload() simplifies to a state reset.
  • ItemTagEditViewModel.fetchData() drops the combine() pairing the item-tag flow with the maximum-name-length flow.
• Tests rewritten to drop the now-removed loginRepository wiring and the dead .copy(maximumNameLength = 100) calls; new maximumNameLength_matchesConstant tests assert against the NatConstants value (100).

Backend dependency

Server may stop emitting maximum_name_length in /shopkeeper/permissions meta (the client no longer reads it).

2. Remove "How To Use" entry from Settings

The Settings screen carried a "How To Use" list item linking to myturntag.com/how — a queue-product help page that no longer matches the substrate-v2 generic CRUD app surface. Drop just the SettingsView list item.

The string resource (R.string.how_to_use), the NatConstants.HOW_TO_USE_URL constant, and the OnboardingView call site are left in place because they are still wired and may be repurposed.

Test plan

• ./gradlew test → BUILD SUCCESSFUL
• ./gradlew assembleDebug → BUILD SUCCESSFUL
• ./gradlew spotlessCheck → BUILD SUCCESSFUL
• ./gradlew lint → BUILD SUCCESSFUL
• Manual emulator smoke test:
  • Create / edit an ItemTag — name field still caps at 100 characters; help text still displays "max 100".
  • Open Settings — the "How To Use" row no longer appears; the rows above and below it still render with correct dividers.

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