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/distribution-board-component-structure-project-command.repository.ts

@@ -22,6 +22,7 @@ import { circuitSections } from "../schema/circuit-sections.js";
 import { distributionBoardComponentProtectionDevices } from "../schema/distribution-board-component-protection-devices.js";
 import { distributionBoardComponents } from "../schema/distribution-board-components.js";
 import { executeProjectCommandTransaction } from "./project-command-transaction.persistence.js";
+import { assertEquipmentIdentifierAvailable } from "./equipment-identifier-uniqueness.persistence.js";
 
 export class DistributionBoardComponentStructureProjectCommandRepository
   implements DistributionBoardComponentStructureProjectCommandStore
@@ -94,6 +95,11 @@ export class DistributionBoardComponentStructureProjectCommandRepository
     if (existing) {
       throw new Error("Distribution-board component id already exists.");
     }
+    assertEquipmentIdentifierAvailable(
+      database,
+      snapshot.component.circuitListId,
+      snapshot.component.equipmentIdentifier
+    );
     database
       .insert(distributionBoardComponents)
       .values(snapshot.component)
@@ -187,6 +193,17 @@ export class DistributionBoardComponentStructureProjectCommandRepository
         "Distribution-board component changed before update."
       );
     }
+    if (
+      target.component.equipmentIdentifier !==
+      expected.component.equipmentIdentifier
+    ) {
+      assertEquipmentIdentifierAvailable(
+        database,
+        expected.component.circuitListId,
+        target.component.equipmentIdentifier,
+        expected.component.id
+      );
+    }
     database
       .update(distributionBoardComponents)
       .set(target.component)