Fix code-review findings across domain, persistence, server and frontend

Full-codebase review turned up five real correctness/security bugs and
a dozen smaller inconsistencies; all are fixed here with matching test
coverage:

- BMK uniqueness silently allowed German-umlaut duplicates ("Ä1" vs
  "ä1") because the DB's normalized index only folds ASCII case. Added
  a shared Unicode-aware pre-check used by every circuit/component
  insert and rename path (one of which had no pre-check at all).
- CircuitDeviceRow.simultaneityFactor had no upper bound at the row
  level (command model and snapshot/restore schema), unlike every
  sibling entity, letting a bad value silently corrupt power totals.
- Grid cell editing silently misread German thousands-separator input
  ("1.500" parsed as 1.5); "." is now rejected outright with a clear
  message instead of guessing.
- The editor's shared command runner (runCommand/applyHistory) had no
  re-entrancy guard, so a double click/drop could fire the same
  command twice and race a BMK collision or revision conflict. Added a
  synchronous ref guard plus isSaving on the buttons that lacked it.
- GET .../next-identifier leaked circuit-numbering state for sections
  in other projects (no ownership check, 400 instead of 404). Moved
  under /projects/:projectId and scoped it.

Also: added the missing circuits.section_id / circuit_device_rows.
circuit_id indexes (migration 0006), gave FormModal a focus trap /
Escape-to-close / focus restore and rebuilt ProjectSettingsModal on
top of it instead of duplicated markup, removed dead code (3 orphaned
domain model files, an unused persistence helper, a wrapper only used
by its own test), pointed the project page at GET /projects/:id
instead of listing+filtering client-side, closed the gap between the
documented 18 MB CSV limit and the ~17.17 MiB actually enforced, added
missing upper bounds on several free-text fields, filled in nine
missing German labels in the revision timeline, replaced a
key-order-fragile JSON.stringify equality check with a real field
comparison, made an implicit sort-order assumption in three
renumbering helpers explicit, cleared the sidebar's target selection
when it no longer resolves after a tree reload, and fixed
updateGlobalDevice to check-then-write instead of write-then-check.

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

src/db/repositories/equipment-identifier-uniqueness.persistence.ts

@@ -0,0 +1,41 @@
+import { eq } from "drizzle-orm";
+import type { AppDatabase } from "../database-context.js";
+import { circuitListEquipmentIdentifiers } from "../schema/circuit-list-equipment-identifiers.js";
+
+export function normalizeEquipmentIdentifier(value: string): string {
+  return value.trim().toLowerCase();
+}
+
+/**
+ * The DB-level normalized unique index uses SQLite's built-in lower(),
+ * which only folds ASCII a-z and leaves German characters (Ä/Ö/Ü/ß/…)
+ * untouched, so it alone would let e.g. "Ä1" and "ä1" coexist. This check
+ * normalizes with JS's Unicode-aware toLowerCase() against every
+ * identifier already registered for the circuit list (circuits and
+ * distribution-board components share one BMK namespace via
+ * circuit_list_equipment_identifiers), catching what the DB index cannot.
+ */
+export function assertEquipmentIdentifierAvailable(
+  database: AppDatabase,
+  circuitListId: string,
+  equipmentIdentifier: string,
+  excludeOwnerId?: string
+): void {
+  const candidate = normalizeEquipmentIdentifier(equipmentIdentifier);
+  const existing = database
+    .select({
+      ownerId: circuitListEquipmentIdentifiers.ownerId,
+      equipmentIdentifier: circuitListEquipmentIdentifiers.equipmentIdentifier,
+    })
+    .from(circuitListEquipmentIdentifiers)
+    .where(eq(circuitListEquipmentIdentifiers.circuitListId, circuitListId))
+    .all();
+  const duplicate = existing.some(
+    (row) =>
+      row.ownerId !== excludeOwnerId &&
+      normalizeEquipmentIdentifier(row.equipmentIdentifier) === candidate
+  );
+  if (duplicate) {
+    throw new Error("Duplicate equipmentIdentifier in circuit list.");
+  }
+}