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/circuit-structure-project-command.repository.ts

@@ -27,6 +27,7 @@ import {
 } from "./circuit-device-row-structure.persistence.js";
 import { executeProjectCommandTransaction } from "./project-command-transaction.persistence.js";
 import { resolveCircuitVoltage } from "./project-voltage.persistence.js";
+import { assertEquipmentIdentifierAvailable } from "./equipment-identifier-uniqueness.persistence.js";
 
 export class CircuitStructureProjectCommandRepository
   implements CircuitStructureProjectCommandStore
@@ -103,24 +104,11 @@ export class CircuitStructureProjectCommandRepository
     if (existingCircuit) {
       throw new Error("Circuit id already exists.");
     }
-    const duplicateIdentifier = database
-      .select({ id: circuits.id })
-      .from(circuits)
-      .where(
-        and(
-          eq(circuits.circuitListId, snapshot.circuitListId),
-          eq(
-            circuits.equipmentIdentifier,
-            snapshot.equipmentIdentifier
-          )
-        )
-      )
-      .get();
-    if (duplicateIdentifier) {
-      throw new Error(
-        "Duplicate equipmentIdentifier in circuit list."
-      );
-    }
+    assertEquipmentIdentifierAvailable(
+      database,
+      snapshot.circuitListId,
+      snapshot.equipmentIdentifier
+    );
 
     if (snapshot.deviceRows.length > 0) {
       const rowIds = snapshot.deviceRows.map((row) => row.id);