feat(bokslut): IL 18 kap pooled tax depreciation with method election (#1393)

* feat(bokslut): IL 18 kap pooled tax depreciation with method election

Rakenskapsenlig (huvudregel 30 / kompletteringsregel 20) and restvarde 25
as a company-level annual pool separate from per-asset book depreciation.
Method election persisted with immutable snapshots and book-conformity
confirmation for rakenskapsenlig.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* chore(db): move tax depreciation migrations to coordinated versions

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(bokslut): keep tax depreciation view loadable when a saved election goes stale

A predecessor's changed closing value can push a saved elected deduction
above the new statutory maximum; the view now falls back to the statutory
recomputation so the snapshot is flagged stale instead of crashing.
Ratchet naive-ore-round baseline down by 3.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(bokslut): resolve tax-depreciation period selects statically

The no-phantom-columns guard counts every select it cannot resolve
toward a hard ceiling, and the PERIOD_COLUMNS join pushed the repo
4 over (364 > 360). Inline the literal column list at the four call
sites so the guard verifies these columns instead of skipping them.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(bokslut): address review findings on tax depreciation election

- DepreciationPanel: gate the saving flag on a dedicated save sequence
  so a successful save (which refreshes the view and bumps the request
  version) no longer leaves the card permanently busy
- computeTaxDepreciation: refuse kompletteringsregel_20 with a positive
  basis and no acquisition cohorts instead of degenerating to a full
  write-off the cohort evidence does not support (IL 18 kap. 17 §)
- migration 227000: judge the asset-method guards on NEW.disposed_at so
  reversing a disposal cannot reactivate a grandfathered non-linear row
- migration 227200: require snapshot column completeness in the CHECK;
  SQL NULL semantics let partially populated snapshots pass the pure
  arithmetic comparisons
- depreciation route: use the string issue code 'custom' like the rest
  of the codebase instead of the Zod 3 compat enum

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

app/api/assets/route.ts

@@ -6,7 +6,7 @@ import { validateBody } from '@/lib/api/validate'
 import { K3ComponentSchema } from '@/lib/api/schemas'
 import { createAsset, listAssets } from '@/lib/bokslut/assets/asset-service'
 import { validateComponents } from '@/lib/bokslut/assets/k3-components'
-import type { AssetCategory, DepreciationMethod } from '@/types'
+import type { AssetCategory, WritableDepreciationMethod } from '@/types'
 
 const ASSET_CATEGORIES: readonly AssetCategory[] = [
   'immaterial',
@@ -19,14 +19,8 @@ const ASSET_CATEGORIES: readonly AssetCategory[] = [
   'other_tangible',
 ] as const
 
-// All four depreciation methods are now implemented by the engine. The DB
-// CHECK constraint mirrors this list (see
-// 20260526120100_restvardeavskrivning.sql).
-const DEPRECIATION_METHODS: readonly DepreciationMethod[] = [
+const DEPRECIATION_METHODS: readonly WritableDepreciationMethod[] = [
   'linear',
-  'declining_balance_30',
-  'declining_balance_20',
-  'restvardesavskrivning_25',
 ] as const
 
 const CreateAssetSchema = z
@@ -40,13 +34,12 @@ const CreateAssetSchema = z
     salvage_value: z.number().nonnegative().optional(),
     useful_life_months: z.number().int().positive(),
     depreciation_method: z
-      .enum(DEPRECIATION_METHODS as unknown as [DepreciationMethod, ...DepreciationMethod[]])
+      .enum(DEPRECIATION_METHODS as unknown as [
+        WritableDepreciationMethod,
+        ...WritableDepreciationMethod[],
+      ])
       .optional(),
-    // Restvärde-target floor for restvärdeavskrivning. Required iff
-    // depreciation_method = 'restvardesavskrivning_25'. The DB CHECK enforces
-    // the same biconditional; we mirror it in the API for an early, Swedish
-    // error message rather than a Postgres check_violation surfacing.
-    restvarde_target: z.number().nonnegative().nullable().optional(),
+    restvarde_target: z.null().optional(),
     bas_asset_account: z.string().regex(/^\d{4}$/).optional(),
     bas_accumulated_account: z.string().regex(/^\d{4}$/).optional(),
     bas_expense_account: z.string().regex(/^\d{4}$/).optional(),
@@ -63,7 +56,6 @@ const CreateAssetSchema = z
     // outside the legitimate range for the asset category so the chart stays
     // BAS-aligned and INK2R mappings continue to work.
     validateBasOverrides(value, ctx)
-    validateRestvardeTarget(value, ctx)
     validateK3Components(value, ctx)
   })
 
@@ -88,45 +80,6 @@ function validateK3Components(
   }
 }
 
-function validateRestvardeTarget(
-  value: {
-    depreciation_method?: DepreciationMethod
-    restvarde_target?: number | null
-    acquisition_cost?: number
-  },
-  ctx: z.RefinementCtx,
-): void {
-  const isRestvarde = value.depreciation_method === 'restvardesavskrivning_25'
-  const hasTarget = value.restvarde_target !== undefined && value.restvarde_target !== null
-  if (isRestvarde && !hasTarget) {
-    ctx.addIssue({
-      code: z.ZodIssueCode.custom,
-      path: ['restvarde_target'],
-      message: 'restvarde_target krävs när avskrivningsmetoden är restvärdeavskrivning (25 %).',
-    })
-  }
-  if (!isRestvarde && hasTarget) {
-    ctx.addIssue({
-      code: z.ZodIssueCode.custom,
-      path: ['restvarde_target'],
-      message: 'restvarde_target får bara anges för restvärdeavskrivning (25 %).',
-    })
-  }
-  if (
-    isRestvarde &&
-    hasTarget &&
-    value.acquisition_cost !== undefined &&
-    (value.restvarde_target as number) >= value.acquisition_cost
-  ) {
-    ctx.addIssue({
-      code: z.ZodIssueCode.custom,
-      path: ['restvarde_target'],
-      message:
-        'restvarde_target måste vara lägre än anskaffningsvärdet: annars finns inget kvar att skriva av.',
-    })
-  }
-}
-
 function validateBasOverrides(
   value: {
     category: AssetCategory