fix(build): give the Vercel type-check worker a 6 GB heap so next build stops stalling at the 45-min cap (#1749)

Four production builds since 2026-08-14 (dpl_Cw4smfRf, dpl_2RPDg4vZ,
dpl_DixYhSW4, dpl_9ECLphY4) and PR #1746's preview died with
BUILD_EXCEEDED_MAXIMUM_TIME. Every log stops at the same line right after a
normal ~92 s compile: "Running TypeScript ...", then nothing for 44 minutes.

The type-check runs in a Next worker that loads the whole tsconfig program
(3,500 files incl. 1,371 tests). Measured locally it needs ~4.5 GB; on the
standard 4-core/8 GB Vercel machine the worker runs at V8's default ~4 GB
heap ceiling, so it sits at the edge and sometimes thrashes in GC forever
instead of failing. Normal builds show it too: the TS phase is 105 s most
of the time and 2.3-2.4 min on the unlucky ones. CI hit the same wall on
2026-08-19 and got NODE_OPTIONS=--max-old-space-size=8192 in core-build.yml;
Vercel never got the equivalent.

vercel.json buildCommand now runs the same npm run build under
NODE_OPTIONS=--max-old-space-size=6144. The worker inherits it (Next creates
it with isolatedMemory: false). buildCommand rather than a project env var
(would also reach function runtime) or build.env (deprecated in the schema).

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

DECISIONS.md

@@ -1117,3 +1117,4 @@ One line per decision: `[YYYY-MM-DD] <decision>: <why>`. Appended by agents and
 [2026-08-20] Reconciliation opens on the FULL year and keeps its own range-preset memory, separate from the shared report-family key. Inheriting a "Denna manad" preset last used on Resultatrapport would show an alarming difference for a window the user never chose on this page, and a part-year reconciliation window answers a question nobody asked.
 [2026-08-20] The matcher now runs automatically once per window+account when there is unmatched work, instead of waiting for a button many users never found. It is a dry run: nothing is written, and Tillampa still requires an explicit click. ?autorun=1 keeps a distinct meaning (run even on a clean window) so the transactions-inbox deep link still produces a result rather than silence.
 [2026-08-20] Unmatched bank rows that no voucher on the account could settle (direction-compatible and equal to the ore) get "Bokfor" linking to /transactions?highlight=<id> instead of a match picker. They are unbooked affarshandelser, not reconciliation work, and the picker held nothing for them. The rule is deliberately strict: a false negative offers booking on a pairable row (a legitimate outcome), a false positive sends the user into an empty picker.
+[2026-08-20] Vercel build heap is raised through vercel.json `buildCommand` (`NODE_OPTIONS=--max-old-space-size=6144 npm run build`), not a project env var and not `build.env`: a project-level NODE_OPTIONS also reaches function runtime (V8 sizes the heap against a limit the function does not have), and `build.env` is marked deprecated in the vercel.json schema; `buildCommand` scopes the flag to the build exactly like core-build.yml's 8192 does for CI. 6144 fits the standard 4-core/8 GB build machine next to the main next process; the type-check needs ~4.5 GB and was hanging at V8's ~4 GB default ceiling (4 production timeouts 2026-08-14..20).

vercel.json

@@ -1,4 +1,5 @@
 {
+  "buildCommand": "NODE_OPTIONS=--max-old-space-size=6144 npm run build",
   "regions": ["arn1"],
   "crons": [
     {