feat(tui): CRUD foundation (form, state, keys, delete ops)

[lvlcn-t]

What

Foundation for adding create/edit/rename/delete to the TUI. This is PR
1 of a stacked series (foundation → tenants → contexts → credentials).
No tab emits CRUD actions yet, so the TUI is behaviorally unchanged;
this PR only lands the plumbing that the per-tab PRs build on.

Contents

• Domain (contexts.Manager): add DeleteTenant and
  DeleteCredential (mirroring DeleteContext via a small shared
  deleteEntry helper). config.Config gains DeleteTenant /
  DeleteCredential. Deleting a tenant/credential still referenced by a
  context is allowed and left for the caller to warn about (agreed
  behaviour; the TUI will surface a status-line warning in a later PR).
• tui/form (new package): a reusable multi-field text-input form —
  focus navigation (tab/shift-tab/↑↓), required + custom validators,
  Submitted{Values} / Canceled{} messages. Fully unit-tested; knows
  nothing about the domain.
• tui/state: add FormView and ConfirmView states, and a
  SetConfig setter to swap the store after a write-triggered reload.
• tui/keys: add Create (n), Edit (e), Rename (r),
  Delete (ctrl+d). ctrl+d chosen k9s-style; verified no collision
  with bubbles/list (which uses plain d/f/pgdown).
• tui/tabs: add CRUD TabAction kinds, tabKeys fields, and a
  Reload() method on every tab to rebuild list items from the current
  store after a write.

Deliberately deferred to PR 2

The contexts.Manager dependency injection into the TUI and the
handleAction CRUD dispatch (plus the ConfirmView model and the
reload() flow) land in PR 2 alongside the tenants tab, which is the
first to exercise them. Keeping them out here avoids shipping unused code.

Testing

• go test -race -count=1 -short ./... — all pass (new tui/form and
  contexts delete tests included).
• Full pre-commit (generate, mod tidy, gofumpt, golangci-lint, gitleaks,
  markdownlint) — green.
• tui confirmed to still import neither cmd, login, nor contexts
  (DI deferred); contexts and login remain leaf packages.
• Smoke-tested the built binary: non-TUI paths unchanged; TUI launch path
  unaffected.

Notes

• Bubble Tea's value-receiver Update/View idiom trips gocritic's
  hugeParam; suppressed with //nolint:gocritic and a note that the
  existing models (details.Viewer, splash.Model) already use pointer
  receivers and a broader refactor is tracked separately.

[github-actions]

File	Coverage
All files	50%	❌
az/azconfig.go	66%	❌
az/client.go	0%	❌
az/client.go	0%	❌
az/commands.go	0%	❌
az/secrets.go	0%	❌
az/secrets.go	15%	❌
cmd/context_view.go	85%	✅
cmd/current.go	80%	✅
cmd/delete_context.go	71%	✅
cmd/get.go	56%	❌
cmd/list.go	46%	❌
cmd/output_flags.go	85%	✅
cmd/rename_context.go	69%	❌
cmd/set_context.go	69%	❌
cmd/set_credential.go	97%	✅
cmd/set_credential.go	80%	✅
cmd/set_tenant.go	95%	✅
cmd/set_tenant.go	57%	❌
cmd/use.go	47%	❌
cmd/view.go	95%	✅
cmd/view.go	48%	❌
config/config.go	91%	✅
config/credential.go	0%	❌
config/credential.go	0%	❌
config/credential.go	64%	❌
config/credential.go	48%	❌
config/keyvault.go	14%	❌
config/loader.go	82%	✅
config/loader.go	79%	✅
config/store.go	69%	❌
config/writer.go	69%	❌
contexts/contexts.go	92%	✅
contexts/contexts.go	82%	✅
internal/gendemo/main.go	0%	❌
internal/gendoc/main.go	0%	❌
keyvault/azure.go	0%	❌
keyvault/azure.go	0%	❌
keyvault/keyvault.go	75%	✅
login/login.go	76%	✅
main.go	0%	❌
output/printer.go	79%	✅
semver/version.go	94%	✅
tui/app.go	0%	❌
tui/app.go	0%	❌
tui/tui.go	0%	❌
tui/details/viewer.go	0%	❌
tui/details/viewer.go	0%	❌
tui/form/form.go	60%	❌
tui/keys/builder.go	80%	✅
tui/keys/keys.go	66%	❌
tui/splash/splash.go	0%	❌
tui/splash/splash.go	0%	❌
tui/state/state.go	0%	❌
tui/state/state.go	0%	❌
tui/styles/azure_renderer.go	0%	❌
tui/styles/azure_renderer.go	0%	❌
tui/styles/styles.go	50%	❌
tui/tabs/browse.go	0%	❌
tui/tabs/browse.go	0%	❌
tui/tabs/context_item.go	0%	❌
tui/tabs/context_item.go	0%	❌
tui/tabs/contexts.go	0%	❌
tui/tabs/contexts.go	0%	❌
tui/tabs/credential_items.go	0%	❌
tui/tabs/credential_items.go	0%	❌
tui/tabs/credentials.go	0%	❌
tui/tabs/list_builder.go	0%	❌
tui/tabs/list_builder.go	0%	❌
tui/tabs/tab.go	0%	❌
tui/tabs/tab.go	0%	❌
tui/tabs/tabs.go	0%	❌
tui/tabs/tabs.go	0%	❌
tui/tabs/tenant_items.go	0%	❌
tui/tabs/tenant_items.go	0%	❌
tui/tabs/tenants.go	0%	❌
wif/factory/factory.go	0%	❌
wif/oauth2/browser.go	0%	❌
wif/oauth2/browser_linux.go	0%	❌
wif/oauth2/cache.go	76%	✅
wif/oauth2/cache.go	79%	✅
wif/oauth2/oauth2.go	25%	❌
wif/oauth2/oauth2.go	59%	❌
wif/options.go	20%	❌

Minimum allowed coverage is 70%

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